Toxic Cyanobacteria Choke Water Systems Around California’s Clear Lake
Toxic blooms are a public health risk and increase water treatment costs.
Researchers from the University of California, Davis, are studying Clear Lake in order to understand how nutrients and water circulate within the lake system. From their research vessel the R/V Ted Frantz, the scientists take water quality samples at seven sites every six to eight weeks. Their results will inform state and local responses to the harmful algal blooms.
The Big Valley Band of Pomo Indians has a sliver of land on the flat, fertile western shores of Clear Lake. The tribe’s Environmental Protection Agency began a cyanobacteria monitoring program in 2014 after an exceptionally bad year for toxic blooms on the lake. The monitoring program has influenced a number of additional state studies as well as drinking water testing requirements for utilities that use the lake as a supply source.
One of the worst spots on the lake for harmful algal blooms is Clear Lake Keys, a residential community connected by artificial canals. Blooms peak in the late summer and early fall, though toxin levels in 2020 remained high through November.
Eighteen drinking water utilities use the lake as a water source. Konocti County Water District, which has an intake at this site, has seen operating and treatment costs rise due to harmful algal blooms. A district with a high poverty rate, Konocti received a $10 million state grant to overhaul its water system. Among the upgrades is an intake that extends farther into the lake, where blooms are less prevalent.
In the last two decades, vineyard plantings around Clear Lake have increased, supplanting the walnut and pear orchards that were the basis of Lake County’s agriculture industry. Marijuana operations, some established illegally, have also become more prominent. Fertilizers and sediment from farm runoff are a rich source of nutrients into Clear Lake, and play a role in the lake’s harmful algal blooms.
In 2018, the Division of Drinking Water found that all public water systems around Clear Lake had treatment systems that were effective barriers against cyanotoxins, but Cajina said the new order will provide more data than that one-time snapshot.
State officials are not the only ones concerned. The U.S. Environmental Protection Agency published health advisories in 2015 for two cyanotoxins: cylindrospermopsin and microcystins. Health advisories are unenforceable guidelines that function as a warning signal to water utilities. Below the exposure level, which is measured in days, years, or a lifetime, no health damage is expected to occur. Utilities are not punished if they exceed the advisory as they would be for formal regulations.
To inform potential regulatory standards that utilities would be required to achieve, the EPA ordered more than 3,400 drinking water providers nationwide to look for the toxins. From 2018 to 2020, these utilities tested their treated water for nine cyanotoxins as well as for total microcystins. Only seven systems reported microcystins levels above the health advisory.
Though few systems had toxins survive the treatment process, the threat still lurks in rivers and lakes. Nutrient levels in waters and soils are already high, and warming temperatures are an added boost to cyanobacteria, says Hans Paerl of the UNC Chapel Hill Institute of Marine Sciences.
“They like global warming,” Paerl, one of the country’s foremost cyanobacteria researchers, told Circle of Blue. “They do better when it’s warmer because their optimal growth temperatures are relatively high. Everything you can think of that we’re currently discussing about climate change pretty much benefits them.”
Costner has witnessed these changes, too. His backyard weather station recorded between 6 and 7 inches of rain last year. Usually the area gets more than 25 inches. Clear Lake is nearly as low today as it was in 2014, when the full force of drought fell upon the state.
Though he is apprehensive about the coming summer, Costner is hopeful that the system renovation, when it is completed in 2023, will provide the district and his customers with better water — his family included.
“I live in my district, I drink my water,” he said. “My grandchildren and my children drink the water. I want to have safe water. I want my community to have safe water.”
Brett writes about agriculture, energy, infrastructure, and the politics and economics of water in the United States. He also writes the Federal Water Tap, Circle of Blue’s weekly digest of U.S. government water news. He is the winner of two Society of Environmental Journalists reporting awards, one of the top honors in American environmental journalism: first place for explanatory reporting for a series on septic system pollution in the United States(2016) and third place for beat reporting in a small market (2014). He received the Sierra Club’s Distinguished Service Award in 2018. Brett lives in Seattle, where he hikes the mountains and bakes pies. Contact Brett Walton