Wednesday June 15, 2022

San Francisco Chronicle

Rising temperatures and stagnant water generally signal trouble for human life, but they make for a great environment for the bright, blue-green scum often found in lakes, rivers and reservoirs that flourishes and blooms in hot weather.

These scum blooms, known as harmful algal blooms, are natural parts of the ecosystem, but can also release toxins that sicken or even kill people and animals. They’re becoming more common as temperatures rise and water systems are starved and disrupted, threatening not only public and wildlife health, but the state’s water supply, as well as beloved recreation areas like Lake Merritt in Oakland.

“With climate change, it’s clear that this issue will get more severe,” said Marisa Van Dyke, a senior environmental scientist with the State Water Resources Control Board working on harmful algal bloom issues. Besides hot weather, a primary cause of the toxic blooms is excess nutrients in bodies of water, which, in California, often come from agricultural runoff.

Nearly 70 California lakes, rivers and reservoirs, including several in the Bay Area, have issued “caution,” “warning” and “danger” advisories so far this year. Eight of those belong in the “danger” category, including Lake Del Valle, a drinking water reservoir and popular recreation site in Alameda County. Officials have suspended swimming at Lake Del Valle’s popular beaches.

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