Recreational Activities at Diamond Valley Lake Temporarily Suspended due to Cyanobacteria

Diamond Valley Lake (DVL) near Hemet in southwest Riverside County, the largest of Metropolitan Water District’s (MWD) reservoirs, has temporarily suspended all recreational activities at the lake due a bloom of cyanobacteria—also known as blue-green algae—covering the lake. The suspension includes all boating, fishing and hiking. Blue-green algae blooms are common this time of year because of the warm weather.

However, MWD officials were quick to assure the public that the blue-green algae affects only recreational activities. They assured the public that the quality of the district’s treated drinking water has not been affected.

“This is a recreation issue, not a drinking water issue,” said Dr. Mic Stewart, Metropolitan’s water quality manager. We don’t want folks coming into contact with or fishing in this water. We are not using DVL as a drinking water source right now. Even if we did, our processes for withdrawing the water from the lake and treating it will ensure its safety.”

Traditionally, several of California’s water bodies are closed each summer due to cyanobacteria/blue-green algae. The current algae bloom at 810,000 acre-feet DVL is one of the largest ever seen at the lake since it opened to the public for recreation in October 2003. The bloom is caused by naturally occurring organisms that have produced large areas of green water and mats of green scum floating on the lake. The bloom is releasing cyanotoxins, which in high concentrations can be harmful to humans and animals, especially when ingested.

MWD officials have indicated that recreational activities at the lake could be suspended for a week or longer. They will continue to monitor the blue-green algae bloom and test cyanotoxin levels and will lift the suspension and allow recreational activities to resume when conditions improve.

The State Water Resources Control Board’s Division of Drinking Water offers a number of publications and resources regarding cyanobacteria/blue-green algae, including:

• Cyanobacteria/Cyanotoxins Basic Information (USEPA) at: https://www.epa.gov/nutrient-policy-data/cyanobacteriacyanotoxins
• Frequently Asked Questions and Resources for Harmful Algal Blooms and Cyanobacterial Toxins (USEPA Region 9) at: https://www.epa.gov/sites/production/files/2015-07/documents/habs_faqs-and-resources_v1-july2015.pdf
• USEPA recommendations for Public Water Systems to Manage Cyanotoxins in Drinking Water at: https://www.epa.gov/ground-water-and-drinking-water/cyanotoxin-tools-public-water-systems
• Information on Cyanobacteria and Cyanotoxins (USEPA) at: https://www.epa.gov/nutrient-policy-data/cyanobacterial-harmful-algal-blooms-water
• A Water Utility Manager’s Guide to Cyanotoxins (AWWA/WRF) at: http://www.waterrf.org/PublicReportLibrary/4548a.pdf
• California Harmful Algal Blooms (SWRCB) at: https://mywaterquality.ca.gov/habs/
• Algal Toxin Risk Assessment and Management Strategic Plan for Drinking Water (USEPA) at: https://www.epa.gov/sites/production/files/2015-11/documents/algal-risk-assessment-strategic-plan-2015.pdf
• Cyanobacteria Assessment Network (CyAN) Project (USEPA/NOAA/NASA/USGS) at: https://www.epa.gov/water-research/cyanobacteria-assessment-network-cyan
• Laboratory Information for Cyanotoxin Analyses (SWRCB): Finish Drinking Water | Source Water at: https://www.waterboards.ca.gov/drinking_water/programs/habs/docs/drinklablist.pdf
• Risk Communication Tool Kit for Cyanotoxins at: http://www.waterrf.org/resources/webcasts/pages/PublicWebcasts-detail.aspx?ItemID=80