Clear Lake, one of California's oldest and most visited lakes, is no longer so clear after an algae bloom turned the water cloudy and green.
NASA images highlight the dramatic change in water quality in this Northern California tourist destination. Clear Lake is located in Lake County, about 120 miles north of San Francisco.
The bloom may be composed of blue-green algae or cyanobacteria, which produce microcystin, “a potent toxin that can irritate the skin and cause liver and kidney damage,” the National Aeronautics and Space Administration wrote.
The image below shows the lake on May 16, 2023 (left) and the same date this year (right). Last year algae levels were significantly lower at this time, as evidenced by the clear change in water colour.
Algae blooms have been common in Clear Lake's long history, but have become more common with human activity in the last century, according to NASA.
“Runoff from nearby farms, vineyards, failing septic systems, gravel mines, and an abandoned open-pit mercury mine contribute to water quality problems in the lake,” NASA wrote.
A satellite image from the National Aeronautics and Space Administration shows Clear Lake in Northern California during an algal bloom on May 15, 2024.
(NASA Earth Observatory, Wanmei Liang)
Additionally, they wrote, some nutrients exist in lakebed sediment and are mixed with the water by waves and non-native carp.
The NASA satellite image below shows the lake in greater detail. The main algae bloom, in the upper left part of the lake, is dark and cloudy.
The image was taken on May 15 during peak visible flowering. Toxicity monitoring data from May 8th has not yet shown flowering and the next sampling will not occur until June 4th.
At 43,000 acres, Clear Lake is the largest natural freshwater lake in California, possibly the oldest lake in North America.
The lake is the centerpiece of several communities in rural Lake County, including Lakeport, Clearlake, Kelseyville, Glenhaven, and several others.
Major attractions — boating, fishing and swimming — may be affected by algae blooms in the coming weeks, officials warn.
