Cyanotoxins in the state’s second-largest freshwater lake soared this month amid a hot, dry summer.
Colorful blooms of cyanobacteria, also called blue-green algae, paint the nearshore waters of Clear Lake, California’s second-largest freshwater lake. Toxin levels in the blooms broke records in this hot, dry summer. Photo courtesy of Frank Costner
- One sample taken from Clear Lake on September 7 showed a record-high concentration of the liver toxin microcystin, at levels 20,000 times higher than EPA guidance for recreational waters.
- A ‘Do Not Drink’ advisory covers about 280 homes and could last a month or more.
- The lake’s cyanotoxin outbreak has interfered with the operation of public drinking water systems.
By Brett Walton, Circle of Blue – September 22, 2021
Amid a withering drought, a severe harmful algal bloom in California’s second-largest freshwater lake is producing exceptionally high toxin levels, resulting in a drinking water emergency for hundreds of residents who draw water directly from Clear Lake.
The colorful but noxious mats of cyanobacteria in the Northern California lake have also led to difficulties for public utilities that have more sophisticated treatment systems than individual households.
Lake County public health officials on September 15 notified residents along the Lower and Oaks arms not to drink water from their private lake intakes. The warning, which could last a month or more, was issued after water samples from those areas showed astronomically high levels of the liver toxin microcystin.
The warning applies to about 280 households that use the lake as a water source and are not connected to a public water system. Boiling water does not kill the toxins. Alternative water supplies for those affected by the advisory are being arranged. Emergency rooms and veterinary clinics have been briefed on symptoms of cyanotoxin exposure, which can be deadly for pets who drink contaminated water.
Surrounded by oak forests and rolling hills about 100 miles north of San Francisco, Clear Lake lives up to its name in the cooler months. In summer and fall, though, harmful algal blooms have plagued the lake for years, clogging the shores, emitting odors akin to sewage, and producing toxins. Local officials expected a bad summer, considering that water and weather conditions were ripe for explosive cyanobacteria growth. The outcome, though, has been far worse than they expected.
Samples taken near Redbud Park on September 7 showed 160,377 micrograms per liter of microcystin, 10 times higher than the lake’s previous record. The reading is more than 20,000 times higher than the U.S. Environmental Protection Agency health advisory for recreational waters where people swim and boat, which is 8 micrograms per liter.
The sample results have been “eye opening,” according to Sarah Ryan, the environmental director for Big Valley Rancheria, a territory of the Big Valley Band of Pomo Indians that sits on the ancient lake’s western shore. Ryan runs a program to sample and test lake water for cyanotoxins.
Redbud Park is one of about 20 sites that Ryan’s team visits every two weeks in bloom season, which begins in June. In the September 7 sampling, a dozen sites were above the EPA advisory for recreational waters. One site posted a record-high reading for anatoxin-a, another cyanotoxin that damages the nervous system.
Ryan has witnessed increasingly severe cyanobacteria outbreaks in the last decade. In 2014, during the last severe drought, she helped start the lake water testing program that has drawn government attention to the degradation of Clear Lake. Last year, she launched a CDC-funded program for testing tap water from the estimated 400 private intakes around the lake.
“A lot of these are vulnerable systems,” Ryan said. They don’t have the same level of treatment for removing contaminants that municipal systems do.
Of the 50 homes participating in the testing program, 90 percent had water this summer that exceeded federal health guidance for microcystin during a one-time sample. That data, in combination with the September 7 lake sampling, led to the county health advisory.
Angela De Palma-Dow with the Lake County Water Resources Department told Circle of Blue that county officials are still determining what criteria to use for lifting the advisory. Household intakes, like private wells, are not covered by federal and state drinking water standards. Besides, there are no mandatory federal drinking water standards for cyanotoxins.
High-Growth Risk
The Clear Lake warning comes during a hot, dry summer in the American West that has triggered dangerous cyanobacteria outbreaks across the region. Blooms have been reported across California, from the Klamath River in the north to Pyramid Lake in the south. In Oregon, health authorities warned pet owners in August to keep their dogs out of the Willamette River in Portland due to toxins. In Washington state, four dogs died this month after drinking water from the Columbia River, and three dogs died from a separate exposure in the Little Spokane River.
Few places in the American West illustrate these hydrological changes like Clear Lake, where noxious, foul-smelling blooms have become a rite of summer — and beyond. Ryan was still finding concerning levels last year at the end of November.
The outbreak in Clear Lake has caused headaches for the operators of public drinking water systems. Frank Costner is the general manager of Konocti County Water District, which supplies drinking water from Clear Lake to 4,500 people. The district’s intake is not far from Redbud Park, where the sky-high microcystin levels were found.
Costner told Circle of Blue that the blooms are a financial strain and a technical obstacle. Chemical costs have climbed two or three times higher than normal. The cyanobacteria produce ammonia as they decompose, which requires extra chlorine to counteract. Staff are working overtime to keep the treatment facilities operating. Because the lake is near a record low, the plant’s water intake is only 3 feet below the surface, which means the pumping system has to work harder.
It’s too much for a small utility in an economically disadvantaged area to handle alone. Costner said he received a commitment letter from the State Water Board for a $657,000 emergency grant. The funds will go toward a booster pump to help draw water from the lake, refurbished water filters, and an emergency water connection with a neighboring system.
Looking at the lake’s vital signs in March — historically low water, above-average heat, scant rain — Costner had a feeling that this year would be testing. But the extreme outcome still surprised him. “I didn’t realize the raw water quality would be this bad,” he said.
The Multimillion-Dollar Question
While Costner wrestles with making water safe to drink, scientists like Dave Caron are attempting to understand the nature of the thousands of cyanobacteria species, only some of which produce toxins – and only under certain conditions.
Cyanobacteria, also known as blue-green algae, are most comfortable in hothouse settings, said Caron, a professor of biological sciences at the University of Southern California and co-chair of a state network of algae researchers. Algae and cyanobacteria like bright sunshine and warm, stagnant water that is saturated with nitrogen and phosphorus. These nutrients, he said, have the same effect on the aquatic blooms as fertilizer on a lawn.
The seemingly recent outburst of these blooms is partly because people have started to track them, Caron said, especially in the wake of the drinking water emergency in Toledo, in 2014, where harmful algae shut down the city’s water treatment system for several days. But the uptick is also because of a change in environment. A warming planet and more nutrients in waterways are what cyanobacteria prefer.
Still, there are the unknowns. Predicting a bloom is much easier than predicting when a bloom will release toxins. That, Caron said, is “the multimillion-dollar question.” One that public officials across the country would also like answered.
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