LAKE COUNTY, Calif. — The Lake County Water Resources and Environmental Health departments, in partnership with Big Valley Rancheria, have issued guidance to community members who draw their drinking water from Clear Lake in light of high cyanotoxin levels in the lake.

This year, due to persistent heat, the partners monitoring water quality conditions are witnessing elevated levels of cyanotoxins in some areas of Clear Lake.

For Lake County residents with individual water systems that draw water directly from the lake using a private intake, drinking water may become unsafe when high levels of toxins are present.

There is no current data on toxin levels in the drinking water from these private intakes; however because of the high levels of cyanotoxins in Clear Lake, officials want to inform the public about precautions needed if you are a resident with an individual water system drawing from Clear Lake.

Residents with individual water systems around Sulphur Bank Mine and the shores of Clear Lake's Lower and Oaks Arms should be particularly cautious, as recent lake monitoring data demonstrated harmful concentrations of cyanotoxins.

Private water systems frequently do not effectively treat for these toxins, based on monitoring conducted through the Cal-WATCH program. 

Lake County’s Public Water Systems, even those whose raw water source is Clear Lake, effectively remove toxins through a multifaceted treatment process.

Tap water from public water systems is continually monitored to maintain compliance with state water quality requirements. Residents are urged to contact their public water system if they would like more information.

If you live outside of those areas, and you have an individual water system with a private intake that draws water directly from Clear Lake, it is important to maintain awareness of current water quality conditions.

Recent monitoring data is available here.

Big Valley EPA’s robust Clear Lake Cyanotoxin Monitoring Program collects samples from testing sites around Clear Lake at biweekly intervals during the summer months.

The most recent sampling on the shoreline of Clear Lake was conducted on July 10, and the tribe also received samples from the lake’s interior testing sites, which were collected by Lake County Water Resources on July 10.

Microscopy conducted on the lake samples determined 11 Locations met the danger threshold for microcystin toxins.

The chart below lists cyanotoxins and potential health effects from exposure to the toxins, along with the most common cyanobacteria producing the toxins. At some levels of cyanotoxin concentration in your drinking water, it is safe to use water to wash hands and shower; at higher levels (>0.3 µg/L), these activities may be harmful to the health of vulnerable individuals.

Please be cautious when bathing infants and young children, as they may swallow water. Do not drink or use water from any appliance connected to your water supply lines. This includes the water and ice dispensers in your refrigerator, freezer and dishwasher.

For households getting their tap water from individual water systems with private intakes from Clear Lake (and who have not previously participated), testing for contaminants such as cyanotoxins, nitrates, coliform bacteria, and herbicides is available through Big Valley EPA’s Cal-WATCH program detailed here: www.cal-watch.org

For additional information about cyanotoxins and harmful algal blooms, please visit the following websites:

• California Harmful Algal Bloom Portal: https://mywaterquality.ca.gov/habs/index.html;
• Centers for Disease Control and Prevention: www.cdc.gov/habs/index.html;
• Environmental Protection Agency: www.epa.gov/cyanohabs;
• Lake County Water Resources Cyanobacteria website.