Mass die off of fish in the waters of Lakeport, California, USA

Fish Kill Alert

Warm water, lack of oxygen and a heavy biomass load in Clear Lake are among the factors that local and state officials believe are behind a fish die-off in the Lakeport area that occurred over the weekend.
Melanie Pressley, who lives on the lake in the north Lakeport area, said the lake looked good on Saturday night, but when she got up Sunday, she saw hundreds of dead fish on the water.
She said there was a wide variety of fish involved in the die-off – “big, small, medium, anything in between.”
Pressley said that in the 10 years she has lived at her current residence in Lakeport, she’s never seen such a die-off, although they’re not uncommon on the lake.
“I’ve heard of it, I’ve never seen it in a big mass like this,” she said.
Carolyn Ruttan of Lake County Water Resources said she got a report of the die-off on Sunday. She confirmed Pressley’s statement that all types of fish were involved.
The area where the die-off occurred starts at Berger Bay, which Ruttan said is the midpoint between north and south Lakeport on the eastern side of Clear Lake, and moves south along the southern part of the lake’s upper arm.
“In my opinion, it’s low oxygen,” Ruttan said of the die-off’s cause.
Ruttan explained that it’s fairly common for such die-offs to occur in the summer when oxygen levels drop, “especially in those coves and little nooks and crannies around our lake where there’s very little water movement.”
She said there was another die-off two to three weeks ago in Cache Creek.
Warm water can’t hold as much dissolved oxygen as cold water, which is why fish dive down deeper, looking for cooler temperatures, Ruttan said.
In such cases, she said boats on the lake help with moving the water and improving conditions.
Pressley said she emailed the California Department of Fish and Wildlife, which sent out a representative on Monday afternoon to visit with her.
She said the Fish and Wildlife staffer also raised the issues of low oxygen levels and heat.
“They’re looking into other things as well,” she said.
Ruttan said another factor is that a cyanobacteria bloom is going on. She said it is prevalent in the Oaks and lower arms and most of the upper arm, even in the middle of the upper arm. 
“This particular cyanobacteria has been blooming off and on since May,” she said.
Ruttan said the cyanobacteria bloom creates oxygen but also uses that oxygen at night. 
The progress of decomposition also requires oxygen, Ruttan said.
“The amount of biomass in our lake right now is enormous,” and much of it is due to that cyanobacteria bloom, Ruttan said.
Some fish in the lake that were introduced and not native – such as threadfin shad – suffer terribly from big temperature and oxygen swings, Ruttan said. In past years there have at times been large threadfin shad die-offs on the lake.
She noted that the bass is one of the most robust fish, although it relies on threadfin shad as a food sources.
Ruttan said often it’s the larger, older fish that get hit the hardest by low oxygen conditions. 
“Seniors are not as able to grab as much oxygen,” she said, explaining that their gills don’t work as well, and because they’re already compromised they just succumb.
Pressley said there is still a big mass of dead fish by her home.
However, she said a group of vultures and pelicans – which she and her family are jokingly calling the “Lakeport cleanup crew” – are doing their part to disperse the fish by eating them.
Courtesy of

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