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Despite Record Snow Melt, Toxic Algae Continues To Bloom In California Lakes And Ponds

California Department of Fish and Wildlife

A blue-green algae (cyanobacteria) bloom at Clear Lake, Lake County, California, resulted in oxygen depletion in the water and the subsequent mortality of multiple aquatic species, including carp, catfish, bluegill and crappie.

California Department of Fish and Wildlife

California’s record snowpack is melting into significant runoff this summer, filling the state’s lakes and ponds with cold, fresh water. These flows usually help prevent blue-green algae blooms, which form in waterways and are toxic to humans and can be deadly to pets. But since mid-spring, there’s been reports of the dangerous — and stinky — algae blooms across the state.

"It's interesting — and maybe a bit surprising — that we do see these blooms even after these big winters,” said Keith Bouma-Gregson, manager of the California Freshwater Harmful Algal Blooms Program

Blooms have been found in lakes such as Shasta and Oroville in the north, and as far south as Lindo Lake near San Diego. 

Bouma-Gregson says the resurgent blooms during the hot summer months could be because of the erosion, which snow-melt runoff carried into reservoirs. 

Blue-green algae, also known as cyanobacteria, is a natural part of ecosystems and has been around for billions of years. It grows in multiple colors — also red, brown and even white — and can look like paint floating on water. And it often smells like rotten eggs.

The algae produces oxygen, and it’s a food source for some organisms. But when conditions align — hot temperatures, still water and increased dirt and debris in that water — algae can grow rapidly and result in blooms. 

Their toxins and compounds pose a risk to humans and animals. Blooms usually happen between April and October, and some research suggests that climate change is making them worse.

“With more droughts, we expect blooms to be prevalent,” said Bouma-Gregson.

Perhaps the worst bloom so far this year is in the middle of the state at San Luis Reservoir, according to Maggie Macias with the Department of Water Resources. 

"There's no swimming, no water contact sports, such as jet skiing, due to potential adverse health effects,” she said. 

Algae can cause skin rashes and vomiting — and in some cases pets will die when exposed. 

A DWR release says pets are “susceptible because they tend to drink while in the water and lick their fur afterward.”

To find a map of harmful algal blooms in California, click here

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