LAKE COUNTY, Calif. — As climate change increases temperatures, harmful algal blooms, or HABs, caused by cyanobacteria are on the rise in lakes, rivers and reservoirs, posing a health threat to humans, domestic animals and wildlife.
A study published this week by the Public Health Institute’s Dr. Gina Solomon and PHI’s Tracking California program revealed that microcystin, a toxin produced by cyanobacteria, contaminated private drinking water that many community members rely on in Lake County.
Clear Lake is the largest freshwater lake in the state, and over 60% of residents in Lake County receive their drinking water from the lake.
An estimated 500 homes around the lake have private drinking water supplies — either lake water intakes or near-shore wells.
“A new study, Harmful Algal Bloom (HAB) Affecting Private Drinking Water Intakes – Clear Lake, California,” published Wednesday in Morbidity and Mortality Weekly Reports, a publication of the Centers for Disease Control and Prevention, found that:
• Microcystins were detected in the tap water of 22 of 31 homes (about 70% of homes tested) with lake water intakes.
• In 18 of the 31 homes (58%) with lake water intakes, the microcystin level was at or above the US Environmental Protection Agency’s drinking water health advisory of 0.3 μg/L (maximum=3.85 μg/L).
• Microcystins were not detected in tap water of any of the homes with near-shore wells.
The researchers noted that 17 public drinking water systems also use lake water, but these systems conducted frequent testing and used water treatment to successfully control the toxins.
The study was a collaborative project between the Public Health Institute, PHI’s Tracking California, Big Valley Band of Pomo Indians, and the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment and State Water Resources Control Board’s Division of Drinking Water.
Referred to as “California Water: Assessment of Toxins for Community Health,” or Cal-WATCH, the study is funded by the CDC’s Environmental Health Capacity program.
Over the past decade, many locations in California and nationwide, including Clear Lake, have experienced an increase in harmful algal blooms.
Cyanotoxins produced by cyanobacteria contaminate the water and can cause illness and even death in humans, domestic animals and wildlife.
“Tribes have always relied on Clear Lake for some basic needs — members use the lake for important cultural activities, it’s a source of food and income, and the wildlife depend on it as well,” said Sarah Ryan, director of the Big Valley Band of Pomo Indians’ Environmental Protection Department and a co-author of the study.
“Our ecosystem is altered because of climate change. Drought and HABs have created severe impacts on our local economy, affecting access to safe drinking water for many people in the Clear Lake area, impairing traditional cultural activities, and creating health issues,” Ryan added.
From June to November 2021, the Cal-WATCH project collected and analyzed tap water samples from households with private lake water intakes and private wells located within 50 feet of the lake and analyzed the tap water samples for microcystin.
Based on initial findings from the Cal-WATCH study and an increase in severity of HABs in Clear Lake, the local health officer issued an emergency advisory in September of 2021, advising community members with private lake water intakes in the Lower and Oaks Arms of the lake “not to drink” their tap water.
State, local and tribal governments coordinated with local public water systems and provided free drinking water filling stations for the affected population.
Although the drinking water advisory was lifted two months later, the severity of the bloom on the lake in 2022 has prompted renewed recreational and private intake drinking water advisories from the local health officer and the tribe.
“We will likely continue to see an increase in HABs due to climate change,” said Dr. Gina Solomon, the lead author of the new study. “This study revealed that households who rely on water directly from an affected lake are at high risk. We are encouraged that agencies are partnering for a united public health response and providing access to free drinking water as a short-term solution.”
The researchers pointed out that long-term solutions are also necessary, including transitioning homes to public water systems, providing ongoing public education, and researching/implementing other strategies to mitigate HABs, including reduction of nutrient run-off, revegetation of shorelines and aeration.