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California sets nation’s first water standard for cancer-causing contaminant

News Feed
Wednesday, April 17, 2024

In summary Water suppliers say the costs will be massive, with rates increasing for many consumers. Known as the “Erin Brockovich” chemical, hexavalent chromium is found statewide. In an effort to protect more than 5 million Californians from a cancer-causing contaminant, state regulators today set a new standard that is expected to increase the cost of water for many people throughout the state.  The State Water Resources Control Board unanimously approved the nation’s first drinking water standard for hexavalent chromium, which is found naturally in some California groundwater as well as water contaminated by industries. Now water suppliers will be forced to install costly treatment to limit the chemical in water to no more than 10 parts per billion — equivalent to about 10 drops in an Olympic-sized swimming pool.  California water systems are expected to spend $180 million a year to comply, including testing and treatment. The water board said the average cost for most people would be less than $20 per month, with 87% paying about $8 per month. The cost rises an average of $135 per month for people served by water agencies with fewer than 100 connections.  Water suppliers warned officials that the costs of complying would hit low-income customers especially hard.  Coachella City Councilman Frank Figueroa said it would cost his city $90 million to install treatment on its wells, which would increase average monthly bills by almost 500% — “an insufferable figure” for the community, where incomes average $24,000 a year per person. Cities and water agencies said they desperately need financial help from the state. “This year’s fiscal crunch does not bode well, and even in a good year, they (state officials) can’t get aid to everyone that needs it,” Tim Worley, managing director of the Community Water Systems Alliance, told CalMatters.  Hexavalent chromium was made infamous by the movie “Erin Brockovich,” which dramatized Pacific Gas & Electric’s contamination of the water supply of a small California desert town. PG&E paid a $333 million settlement to about 600 Hinkley residents in 1996 who claimed they suffered high rates of cancer and other diseases. Levels above the new state limit have been reported in about 330 sources of water supplies in California. Some of the areas affected are the counties of Sacramento, Solano, Santa Cruz, San Bernardino, Santa Barbara, Monterey and Merced. The highest levels found were in Riverside, Yolo, Los Angeles and Ventura counties, although water suppliers may blend or treat the water to reduce the contaminants there. Central Coast resident Ana Maria Perez told the board that her community suffers from elevated levels of hexavalent chromium, nitrates and other contaminants.  “I’m here because the State Water Board has again failed us,” she said through an interpreter. “It’s not fair that many people have to get sick and even die because the State Water Board has not done their job well.” The largest water suppliers will have two years to comply; smaller ones with fewer than 1,000 connections will have four years. Many water suppliers said permitting, financing and construction timelines would make it difficult to meet these deadlines, and urged the state for more flexibility.  “It’s untenable for some of those communities,” said Andrea Abergel, manager of water policy for the California Municipal Utilities Association.  The new standard is one of the least protective of all the water contaminants regulated by California, according to a state analysis.  Public health advocates had urged a more stringent standard because the one set is 500 times higher than the level that state scientists deemed a negligible, one-in-a-million cancer risk. Under the new standard, for every 2,000 people who drink the water for a lifetime, one person would be at risk of cancer.   “Personally, I think we should go lower,” said water board member Laurel Firestone. She voted for it anyway but wants to revisit it when the standard is reviewed in five years.  Max Costa, professor and chair of environmental medicine at NYU School of Medicine, was an expert witness for residents in the Brockovich case. When California regulators first unveiled the proposed limit, he said “it’s not terrible, but it’s not acceptable…The most acceptable level is none.”  Some hexavalent chromium occurs naturally in California’s rocks and soils; some seeps into the environment from industries that work with chrome, such as metal-plating, stainless steel production and wood preservation.  California’s new standard is “expected to protect an estimated 5.5 million people… from potential illness due to hexavalent chromium,” according to a water board report.  California until now limited hexavalent chromium under a combined standard of 50 parts per billion for all types of chromium, including a more benign type called trivalent chromium. The U.S. Environmental Protection Agency doesn’t have a hexavalent chromium standard for drinking water. Instead, more than 30 years ago, it set a national standard for total chromium at 100 parts per billion, or 10 times higher than the California one for hexavalent chromium. In response to studies linking it to cancer, the EPA is now conducting a human health risk assessment for the contaminant. A decade ago, California regulators tried to enact the same limit for hexavalent chromium but the regulation was overturned in court because it “failed to properly consider the economic feasibility of complying.”  California regulators said their analysis now supports the feasibility because of the low per-person costs for most people and “because there are sufficient resources available.” They added, though, that they can’t guarantee state funding to assist water suppliers. “Those same dollars are spoken for time and time again,” water board member Sean Maguire said at the hearing today. “Which is why we have so many folks who still are struggling meeting even the current standards that we have today.”  Hexavalent chromium has long been known to cause cancer when it’s inhaled, but until recently it was controversial whether drinking it also was linked to cancer. In 2008, s study showed that rats and mice drinking high doses grew cancers in their mouths and intestines, which scientists say "clearly demonstrates” a cancer risk from consuming it. Roberta Walker, a former resident of Hinkley, blames the contaminant for health problems that have plagued her family and community. The levels of contamination in Hinkley were far higher than the limits the state adopted today. But even California’s new limits, Walker said, are too high.  “I don’t care if it’s a pinch or a lot. A poison is poison,” Walker said. “No matter how you look at it, it’s not good.” 

Water suppliers say the costs will be massive, with rates increasing for many consumers. Known as the “Erin Brockovich” chemical, hexavalent chromium is found statewide.

In summary

Water suppliers say the costs will be massive, with rates increasing for many consumers. Known as the “Erin Brockovich” chemical, hexavalent chromium is found statewide.

In an effort to protect more than 5 million Californians from a cancer-causing contaminant, state regulators today set a new standard that is expected to increase the cost of water for many people throughout the state. 

The State Water Resources Control Board unanimously approved the nation’s first drinking water standard for hexavalent chromium, which is found naturally in some California groundwater as well as water contaminated by industries.

Now water suppliers will be forced to install costly treatment to limit the chemical in water to no more than 10 parts per billion — equivalent to about 10 drops in an Olympic-sized swimming pool

California water systems are expected to spend $180 million a year to comply, including testing and treatment. The water board said the average cost for most people would be less than $20 per month, with 87% paying about $8 per month. The cost rises an average of $135 per month for people served by water agencies with fewer than 100 connections. 

Water suppliers warned officials that the costs of complying would hit low-income customers especially hard. 

Coachella City Councilman Frank Figueroa said it would cost his city $90 million to install treatment on its wells, which would increase average monthly bills by almost 500% — “an insufferable figure” for the community, where incomes average $24,000 a year per person.

Cities and water agencies said they desperately need financial help from the state.

“This year’s fiscal crunch does not bode well, and even in a good year, they (state officials) can’t get aid to everyone that needs it,” Tim Worley, managing director of the Community Water Systems Alliance, told CalMatters. 

Hexavalent chromium was made infamous by the movie “Erin Brockovich,” which dramatized Pacific Gas & Electric’s contamination of the water supply of a small California desert town. PG&E paid a $333 million settlement to about 600 Hinkley residents in 1996 who claimed they suffered high rates of cancer and other diseases.

Levels above the new state limit have been reported in about 330 sources of water supplies in California. Some of the areas affected are the counties of Sacramento, Solano, Santa Cruz, San Bernardino, Santa Barbara, Monterey and Merced. The highest levels found were in Riverside, Yolo, Los Angeles and Ventura counties, although water suppliers may blend or treat the water to reduce the contaminants there.

Central Coast resident Ana Maria Perez told the board that her community suffers from elevated levels of hexavalent chromium, nitrates and other contaminants. 

“I’m here because the State Water Board has again failed us,” she said through an interpreter. “It’s not fair that many people have to get sick and even die because the State Water Board has not done their job well.”

The largest water suppliers will have two years to comply; smaller ones with fewer than 1,000 connections will have four years. Many water suppliers said permitting, financing and construction timelines would make it difficult to meet these deadlines, and urged the state for more flexibility. 

“It’s untenable for some of those communities,” said Andrea Abergel, manager of water policy for the California Municipal Utilities Association. 

The new standard is one of the least protective of all the water contaminants regulated by California, according to a state analysis. 

Public health advocates had urged a more stringent standard because the one set is 500 times higher than the level that state scientists deemed a negligible, one-in-a-million cancer risk. Under the new standard, for every 2,000 people who drink the water for a lifetime, one person would be at risk of cancer.  

“Personally, I think we should go lower,” said water board member Laurel Firestone. She voted for it anyway but wants to revisit it when the standard is reviewed in five years. 

Max Costa, professor and chair of environmental medicine at NYU School of Medicine, was an expert witness for residents in the Brockovich case. When California regulators first unveiled the proposed limit, he said “it’s not terrible, but it’s not acceptable…The most acceptable level is none.” 

Some hexavalent chromium occurs naturally in California’s rocks and soils; some seeps into the environment from industries that work with chrome, such as metal-plating, stainless steel production and wood preservation. 

California’s new standard is “expected to protect an estimated 5.5 million people… from potential illness due to hexavalent chromium,” according to a water board report. 

California until now limited hexavalent chromium under a combined standard of 50 parts per billion for all types of chromium, including a more benign type called trivalent chromium.

The U.S. Environmental Protection Agency doesn’t have a hexavalent chromium standard for drinking water. Instead, more than 30 years ago, it set a national standard for total chromium at 100 parts per billion, or 10 times higher than the California one for hexavalent chromium. In response to studies linking it to cancer, the EPA is now conducting a human health risk assessment for the contaminant.

A decade ago, California regulators tried to enact the same limit for hexavalent chromium but the regulation was overturned in court because it “failed to properly consider the economic feasibility of complying.” 

California regulators said their analysis now supports the feasibility because of the low per-person costs for most people and “because there are sufficient resources available.” They added, though, that they can’t guarantee state funding to assist water suppliers.

“Those same dollars are spoken for time and time again,” water board member Sean Maguire said at the hearing today. “Which is why we have so many folks who still are struggling meeting even the current standards that we have today.” 

Hexavalent chromium has long been known to cause cancer when it’s inhaled, but until recently it was controversial whether drinking it also was linked to cancer. In 2008, s study showed that rats and mice drinking high doses grew cancers in their mouths and intestines, which scientists say "clearly demonstrates” a cancer risk from consuming it.

Roberta Walker, a former resident of Hinkley, blames the contaminant for health problems that have plagued her family and community. The levels of contamination in Hinkley were far higher than the limits the state adopted today. But even California’s new limits, Walker said, are too high. 

“I don’t care if it’s a pinch or a lot. A poison is poison,” Walker said. “No matter how you look at it, it’s not good.” 

Read the full story here.
Photos courtesy of

Thirsty work: how the rise of massive datacentres strains Australia’s drinking water supply

The demand for use in cooling in Sydney alone is expected to exceed the volume of Canberra’s total drinking water within the next decadeSign up for climate and environment editor Adam Morton’s free Clear Air newsletter hereAs Australia rides the AI boom with dozens of new investments in datacentres in Sydney and Melbourne, experts are warning about the impact these massive projects will have on already strained water resources.Water demand to service datacentres in Sydney alone is forecast to be larger than the volume of Canberra’s total drinking water within the next decade. Continue reading...

As Australia rides the AI boom with dozens of new investments in datacentres in Sydney and Melbourne, experts are warning about the impact these massive projects will have on already strained water resources.Water demand to service datacentres in Sydney alone is forecast to be larger than the volume of Canberra’s total drinking water within the next decade.In Melbourne the Victorian government has announced a “$5.5m investment to become Australia’s datacentre capital”, but the hyperscale datacentre applications on hand already exceed the water demands of nearly all of the state’s top 30 business customers combined.Technology companies, including Open AI and Atlassian, are pushing for Australia to become a hub for data processing and storage. But with 260 datacentres operating and dozens more in the offing, experts are flagging concerns about the impact on the supply of drinking water.Sydney Water has estimated up to 250 megalitres a day would be needed to service the industry by 2035 (a larger volume than Canberra’s total drinking water).Cooling requires ‘huge amount of water’Prof Priya Rajagopalan, director of the Post Carbon Research Centre at RMIT, says water and electricity demands of datacentres depend on the cooling technology used.“If you’re just using evaporative cooling, there is a lot of water loss from the evaporation, but if you are using sealers, there is no water loss but it requires a huge amount of water to cool,” she says.While older datacentres tend to rely on air cooling, demand for more computing power means higher server rack density so the output is warmer, meaning centres have turned to water for cooling .The amount of water used in a datacentre can vary greatly. Some centres, such as NextDC, are moving towards liquid-to-chip cooling, which cools the processor or GPU directly instead of using air or water to cool the whole room.NextDC says it has completed an initial smaller deployment of the cooling technology but it has the capacity to scale up for ultra-high-density environments to allow for greater processing power without an associated rise in power consumption because liquid cooling is more efficient. The company says its modelling suggests power usage effectiveness (PUE, a measure of energy efficiency) could go as low as 1.15. Sign up to get climate and environment editor Adam Morton’s Clear Air column as a free newsletterThe datacentre industry accounts for its sustainability with two metrics: water usage effectiveness (WUE) and power usage effectiveness (PUE). These measure the amount of water or power used relative to computing work.WUE is measured by annual water use divided by annual IT energy use (kWh). For example, a 100MW datacentre using 3ML a day would have a WUE of 1.25. The closer the number is to 1, the more efficient it is. Several countries mandate minimum standards. Malaysia has recommended a WUE of 1.8, for example.But even efficient facilities can still use large quantities of water and energy, at scale.NextDC’s PUE in the last financial year was 1.44, up from 1.42 the previous year, which the company says “reflects the dynamic nature of customer activity across our fleet and the scaling up of new facilities”.Calls for ban on use of drinking waterSydney Water says its estimates of datacentre water use are being reviewed regularly. The utility is exploring climate-resilient and alternative water sources such as recycled water and stormwater harvesting to prepare for future demand.“All proposed datacentre connections are individually assessed to confirm there is sufficient local network capacity and operators may be required to fund upgrades if additional servicing is needed,” a Sydney Water spokesperson says.In its submission to the Victorian pricing review for 2026 to 2031, Melbourne Water noted that hyperscale datacentre operators that have put in applications for connections have “projected instantaneous or annual demands exceeding nearly all top 30 non-residential customers in Melbourne”.“We have not accounted for this in our demand forecasts or expenditure planning,” Melbourne Water said.It has sought upfront capital contributions from the companies so the financial burden of works required “does not fall on the broader customer base”.Greater Western Water in Victoria had 19 datacentre applications on hand, according to documents obtained by the ABC, and provided to the Guardian.skip past newsletter promotionSign up to Clear Air AustraliaAdam Morton brings you incisive analysis about the politics and impact of the climate crisisPrivacy Notice: Newsletters may contain information about charities, online ads, and content funded by outside parties. If you do not have an account, we will create a guest account for you on theguardian.com to send you this newsletter. You can complete full registration at any time. For more information about how we use your data see our Privacy Policy. We use Google reCaptcha to protect our website and the Google Privacy Policy and Terms of Service apply.after newsletter promotionThe Concerned Waterways Alliance, a network of Victorian community and environment groups, has flagged its concerns about the diversion of large volumes of drinking water to cool servers, when many of the state’s water resources are already stretched.Cameron Steele, a spokesperson for the alliance, says datacentre growth could increase Melbourne’s reliance on desalinated water and reduce water available for environmental flows, with the associated costs borne by the community. The groups have called for a ban on the use of drinking water for cooling, and mandatory public reporting of water use for all centres.“We would strongly advocate for the use of recycled water for datacentres rather than potable drinking water.”Closed-loop coolingIn hotter climates, such as large parts of Australia during the summer months, centres require more energy or water to keep cool.Danielle Francis, manager of customer and policy at the Water Services Association of Australia, says there isn’t a one-size-fits-all approach for how much energy and water datacentres use because it will depend on the local constraints such as land, noise restrictions and availability of water.“We’re always balancing all the different customers, and that’s the need for residential areas and also non-residential customers, as well as of course environmental needs,” Francis says.“It is true that there are quite a lot of datacentre applications. And the cumulative impact is what we have to plan for … We have to obviously look at what the community impact of that is going to be.“And sometimes they do like to cluster near each other and be in a similar location.”One centre under construction in Sydney’s Marsden Park is a 504MW datacentre spanning 20 hectares, with six four-storey buildings. The CDC centre will become the largest data campus in the southern hemisphere, the company has boasted.In the last financial year, CDC used 95.8% renewable electricity in its operational datacentres, and the company boasts a PUE of 1.38 and a WUE of 0.01. A spokesperson for the company says it has been able to achieve this through a closed-loop cooling system that eliminates ongoing water draw, rather than relying on the traditional evaporative cooling systems.“The closed-loop systems at CDC are filled once at the beginning of their life and operate without ongoing water draw, evaporation or waste, ensuring we are preserving water while still maintaining thermal performance,” a spokesperson says.“It’s a model designed for Australia, a country shaped by drought and water stress, and built for long-term sustainability and sets an industry standard.”Planning documents for the centre reveal that, despite CDC’s efforts, there remains some community concern over the project.In a June letter, the acting chief executive of the western health district of New South Wales, Peter Rophail, said the development was too close to vulnerable communities, and the unprecedented scale of the development was untested and represented an unsuitable risk to western Sydney communities.“The proposal does not provide any assurance that the operation can sufficiently adjust or mitigate environmental exposures during extreme heat weather events so as not to pose an unreasonable risk to human health,” Rophail said.

Costa Rica’s La Fortuna Waterfall Ranks in Top 1% Globally on TripAdvisor

La Fortuna Waterfall in Costa Rica received TripAdvisor’s “Best of the Best” award for the second straight year in the Travellers’ Choice 2025 rankings. This honor places the site among the top 1% of attractions globally, based on millions of traveler reviews and ratings. The waterfall, a key draw in the Arenal Volcano National Park […] The post Costa Rica’s La Fortuna Waterfall Ranks in Top 1% Globally on TripAdvisor appeared first on The Tico Times | Costa Rica News | Travel | Real Estate.

La Fortuna Waterfall in Costa Rica received TripAdvisor’s “Best of the Best” award for the second straight year in the Travellers’ Choice 2025 rankings. This honor places the site among the top 1% of attractions globally, based on millions of traveler reviews and ratings. The waterfall, a key draw in the Arenal Volcano National Park area, attracted roughly 1,000 visitors daily in 2024. The waterfall is about 4 kilometers from the center of La Fortuna in San Carlos, the 70-meter cascade requires a descent of about 530 steps to reach its base. The path includes safety rails, rest spots, and water stations amid native forest trees. At the site, travelers find a restaurant, gift shops, restrooms, and other services. Admission costs $10 for Costa Rican nationals and $20 for international visitors, with reduced rates for those with disabilities. A non-profit group, the Integral Development Association of La Fortuna (ADIFORT), oversees the site. Founded in 1969, ADIFORT directs revenue toward road improvements, environmental care, education, sports, cultural programs, town upkeep, and safety measures. This model ties tourism directly to local progress. The area forms part of a 210-acre biological reserve in premontane tropical wet forest, at 520 meters above sea level. It marks the headwaters of the La Fortuna River. Along the trail, visitors pass an orchid path, butterfly garden, frog habitat, and bee hotel, adding to the natural appeal. Travelers like to visit the waterfall for its clear waters and the chance to swim at the base, though heavy rains can limit access during the rainy season. Reviews highlight the well-maintained facilities and the rewarding hike, despite the steep return climb. The award reflects consistent high marks for the experience, solidifying our country’s reputation in ecotourism. Officials note that sustainable management keeps the site pristine while benefiting residents. As visitor numbers grow, the focus remains on balancing tourism with conservation. This latest win shows the waterfall’s role in showcasing not only Costa Rica’s biodiversity but also our community-driven initiatives. The post Costa Rica’s La Fortuna Waterfall Ranks in Top 1% Globally on TripAdvisor appeared first on The Tico Times | Costa Rica News | Travel | Real Estate.

People living along polluted Thames file legal complaint to force water firm to act

Residents claim raw sewage and poorly treated effluent as result of Thames Water’s failings are threat to healthCommunities across south-east England are filing the first coordinated legal complaints that sewage pollution by Thames Water negatively affects their lives.Thames Water failed to complete upgrades to 98 treatment plants and pumping stations which have the worst records for sewage pollution into the environment, despite a promise to invest in them over the last five years. Continue reading...

Communities across south-east England are filing the first coordinated legal complaints that sewage pollution by Thames Water negatively affects their lives.Thames Water failed to complete upgrades to 98 treatment plants and pumping stations which have the worst records for sewage pollution into the environment, despite a promise to invest in them over the last five years.People in 13 areas including Hackney, Oxford, Richmond upon Thames and Wokingham are sending statutory nuisance complaints to their local authorities demanding accountability from Thames Water and urgent action.At several sites it is not just raw sewage from storm overflows that causes pollution but also the quality of treated effluent coming from Thames Water facilities, which presents a direct threat to public health, the campaigners say.At Thames’s Newbury sewage treatment plant, raw effluent discharges into the River Kennet, a protected chalk stream. Data shows raw sewage discharges from the plant increased by 240% between 2019 and 2024 from 482 hours to 1,630 hours. Thames says the plant is among its 26 most polluting sites.Thames wants the water regulator, Ofwat, to allow it to charge customers £1.18bn over the next five years for the upgrades it has failed to carry out. But the regulator has refused to let it pass the full cost on to customers, allowing only £793m, as it deems bill payers have already funded the upgrades. It says any escalation of costs should be borne by Thames Water.With the company failing to act, people living in the catchment are turning to statutory nuisance complaints under section 79 of the Environmental Protection Act 1990. In letters to their local authorities, they are asking for decisive action by Thames to stop its sewage pollution that is causing harm along the river.A statutory nuisance is an activity that unreasonably interferes with the use or enjoyment of land and is likely to cause prejudice or injury to health.Those living in the area say sewage pollution from Thames’s failing sites and infrastructure has made rivers unsafe and disrupted recreation, sport, local businesses and everyday enjoyment.They cite a 16-year-old rower from Henley rowing club who became unwell after training on the river; tests confirmed he had contracted E coli. His illness coincided with his GCSE exams, preventing him from revising and sitting some papers.In West Berkshire, people are highlighting the case of a kayaker who capsized and became unwell over the following days. And at Tagg’s Island in Hampton, south-west London, five children became ill after playing in the River Thames near Hurst Park.Laura Reineke, who lives in Henley-on-Thames and founded the campaign group Friends of the Thames, said: “People here are fed up with living beside a river that’s being treated like an open sewer. We’ve submitted a nuisance complaint to our local authority because what Thames Water is doing is unacceptable.”Citizen testing of the river has found treated effluent leaving the Henley plant has contained E coli at levels 30 times higher than bathing water safe levels, calculated using Thames Water’s data released under an environmental information request.“Local residents are angry and determined to hold this company accountable for the damage it’s causing to our river and our community,” Reineke said.Thames has already received a record £104m fine by Ofwat over environmental breaches involving sewage spills across its network, after failing to operate and manage its treatment works and wastewater networks effectively.Amy Fairman, the head of campaigns at River Action, which is supporting the coordinated complaints, said: “This action is about fixing sewage pollution in the Thames for good, not compensating people for past failings.“Each local authority must investigate these complaints and, where statutory nuisance is found to exist, issue an abatement notice and take enforcement action. Councils now have a legal duty to act.”She said there was extensive evidence of performance failures at Thames Water, which was on the brink of insolvency. Despite this ministers had not put the company into special administration, a process that would allow for urgent infrastructure upgrades, put public interest ownership and governance first, and protect communities and the environment.Thames Water was approached for comment.

Gold clam invasion in NZ threatens drinking water for millions of people

The invasion threatens more than water. Clams could foul dam intakes and reduce hydroelectric efficiency in a river that generates 13% of New Zealand’s power.

Michele Melchior, CC BY-NDAs a geochemist studying New Zealand’s freshwater systems, I’ve spent years tracking the subtle chemical shifts in our rivers and lakes. But nothing prepared me for the rapid transformation unfolding in the Waikato River since the invasion of the Asian clam (Corbicula fluminea, also known as the freshwater gold clam). First detected in May 2023 in Lake Karāpiro, a reservoir lake on the Waikato, this bivalve is now altering the river’s chemistry in ways that could jeopardise drinking water for up to two million people, disrupt hydroelectric power and undermine decades of ecosystem restoration efforts. Our team’s work reveals how these clams are depleting essential minerals like calcium from the water, impairing arsenic removal during treatment and signalling a rapid escalation with broader impacts ahead. Gold clams now dominate the river bed in many areas, with densities exceeding 1,000 individuals per square metre. Michele Melchior, CC BY-ND Native to eastern Asia, the gold clam can self-fertilise and spreads via contaminated gear, birds or floods. Climate change will likely accelerate its invasion. The problem is already spreading quickly beyond the Waikato River. A recent detection in a Taranaki lake has led to waterway closures. And warnings for the Whanganui River underscore the urgent need for national vigilance. A silent invasion with big consequences The Waikato River stretches 425 km from Lake Taupō to the Tasman Sea, powering nine hydroelectric dams and supplying drinking water to Auckland, Hamilton and beyond. It’s a taonga (cultural treasure) central to Māori identity and the subject of a landmark restoration strategy, Te Ture Whaimana o Te Awa o Waikato, that aims to revive the river’s mauri (life force). In late 2024, arsenic levels in treated Waikato water briefly exceeded safe limits of 0.01 milligrams per litre (mg/L), triggering alarms at treatment plants. Investigations ruled out typical culprits such as geothermal spikes. Instead, our analysis points to the clams. By filtering water and building calcium carbonate shells, the clams are drawing down dissolved calcium by 25% below historical norms. But calcium is crucial for water treatment processes because it helps bind and remove contaminants such as arsenic. Our modelling estimates the clams are forming up to 30 tonnes of calcium carbonate daily in Lake Karāpiro alone. This suggests lake-wide densities averaging around 300 individuals per square metre. 2025 surveys show hotspots with up to 1,134 clams per square metre. The result? Impaired arsenic removal. Without stable calcium, flocs (clumps of particles) don’t form properly, letting arsenic slip through. While the exceedances were short-lived and contained through quick adjustments, they exposed vulnerabilities in a system optimised for historically consistent river chemistry. Field teams survey the rapidly expanding population of freshwater gold clams in the Waikato River. Michele Melchior, CC BY-ND How the clams are changing the river The gold clam isn’t just a filter-feeder; it’s an ecosystem engineer. Each clam can process up to a litre of water per hour, sequestering calcium for shells while releasing ammonia and bicarbonate. Our data from 2024-2025, collected at multiple sites, show these shifts are most pronounced in deeper waters. Statistical tests confirm patterns absent in pre-invasion records. Longer residence times in the reservoir lake (up to seven days) exacerbate the issue. Faster flushing correlates with higher growth rates, as clams ramp up activity. But prolonged retention in warmer months can lead to hypoxia (low oxygen), with the potential to trigger mass die-offs that release toxins or mobilise sediment-bound arsenic. Lake Karāpiro water column temperature and dissolved oxygen levels (from November 2024 to October 2025) show oxygen depletion in deep water during warmer summer conditions, likely exacerbated by the gold clam. Author provided, CC BY-NC-ND These changes threaten more than water treatment. Clams could biofoul dam intakes and reduce hydroelectric efficiency in a river that generates 13% of New Zealand’s power (25% at peak). Native species like kākahi (freshwater mussels) face competition and shifts in nutrient cycling could fuel algal blooms, clashing with restoration goals. Climate risks and stressors in a warming world Amid these ongoing changes, climate projections indicate that hot, dry events – such as prolonged heatwaves or droughts – are likely to become more frequent. Such conditions could reduce river flows and elevate water temperatures, lowering dissolved oxygen levels and creating low-oxygen zones. If clam densities continue to rise exponentially, a mass die-off might occur. This would release pulses of ammonia and organic matter that further deplete dissolved oxygen. This, in turn, could promote arsenic mobilisation from sediments and harmful algal blooms in nutrient-enriched, stagnant waters. This could necessitate supply restrictions for affected communities. Ecologically, it might kill fish and disrupt native biodiversity. Economically, it could interrupt industries reliant on the river. From the Waikato to a nationwide threat The invasion isn’t contained. The clam, which can produce up to 70,000 juveniles annually, thrives in warm, nutrient-rich waters. It is notoriously hard to eradicate once established. In mid-November, the Taranaki Regional Council confirmed the gold clam in Lake Rotomanu. Just days later, warnings were issued to boaties on the Whanganui River, urging rigorous “check, clean, dry” protocols. Without intervention, the clams could reach other systems, including the Clutha or Waitaki, and compound pressures on New Zealand’s already stressed freshwaters. Our research highlights the need for integrated action. Monitoring should expand, incorporating environmental DNA for early detection and calcium isotope tracing to pinpoint clam impacts. Water providers could trial calcium dosing during peak growth periods. But solutions must honour Te Tiriti o Waitangi principles. Collaboration with iwi and blending mātauranga Māori (indigenous knowledge) with science, such as using tikanga indicators for water health, is essential. Biosecurity measures including gear decontamination campaigns are critical to slow spread. Field teams are counting invasive gold clams on the banks of the Waikato River. Michele Melchior, CC BY-ND This invasion intersects with New Zealand’s evolving water policy framework, particularly the Local Water Done Well regime which replaced the repealed Three Waters reforms in late 2023. Councils are now implementing delivery plans and focusing on financial sustainability and infrastructure upgrades. The Water Services Authority Taumata Arawai continues as the national regulator, enforcing standards amid an estimated NZ$185-260 billion infrastructure deficit. Recent government announcements propose further streamlining, including replacing regional councils with panels of mayors or territories boards, while encouraging amalgamations to simplify planning and infrastructure delivery. These changes aim to make local government more cost-effective and responsive to issues such as housing growth and infrastructure funding. But a hot or dry event could test the effectiveness of water policy, potentially straining inter-council coordination for shared resources such as the Waikato River and highlighting gaps in emergency response. Globally, the gold clam has cost billions in damages. New Zealand can’t afford to wait. By acting now, we can protect Te Awa o Waikato and safeguard water security for generations. Adam Hartland receives funding from the Ministry of Business, Innovation and Employment via grant LVLX2302.

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