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As many as 1 million fish suffocate at Lake Elsinore

The Press-Enterprise 7/27/09 by Gene Ghiotto

Hundreds of thousands of fish washed ashore at Lake Elsinore in a die-off Sunday that a state biologist said was caused by an oxygen-diminishing algae bloom nourished by triple-digit temperatures.

The die-off comes as the city and the Lake Elsinore and San Jacinto Watersheds Authority are spending up to $11,000 to promote fishing in the lake through the airing of a 30-minute video on Fox Sports West. The city's share is $7,500.

Between 500,000 and 1 million thumb-size shad and about 6,000 larger fish such as carp and crappie died, Pat Kilroy, director of Lake and Aquatic Resources for Lake Elsinore, said Monday.

"It appears to have subsided at this time," Kilroy said.

It is the first major die-off at the lake since 80 tons of fish perished in 2002 from lack of oxygen and low water levels. In 1998, hundreds of thousands of shad washed up dead. In 1997, about 30 tons of shad died. It's also the first large die-off since the Watersheds Authority two years ago installed an aeration system that pumps air into the lake and installed mixing fans to increase oxygen levels throughout the lake.

Kilroy said he saw signs Monday that the die-off was over.

"Oxygen levels are at their lowest early in the morning," he said. "You'll see fish at the surface gulping for air. There were no fish at the surface."

City crews were scooping up the fish Monday. The fishing areas and beaches are expected to be clear by today, Kilroy said.

The fish are being taken to the El Sobrante Landfill southeast of Corona, said Mark Dennis, a spokesman for the city of Lake Elsinore.

While the number of dead fish appears to be high, Kilroy said, they represent a small percentage of the fish in the lake. The lake holds about 10,000 shad per acre of surface area, Kilroy said. There are 50 to 100 larger fish per acre. The lake's surface area is about 3,000 acres.

Scientists are studying the lake's oxygen and algae levels to determine exactly what caused the die-off, said Mark Norton, administrator for the Watersheds Authority.

The algae bloom and the temperatures over 100 degrees the past few days, appear to be the likely culprits.

Tim Hovey, a fish and game biologist, said plantlike algae blooms are caused by the introduction of nutrients such as phosphorous into the water. In Lake Elsinore's case, it comes from the San Jacinto Mountains, according to the Watersheds Authority. Carp and other large fish at the bottom of the lake stir up nutrients, which feed the algae, which grows better as water temperature increases. As the algae eventually die, it lowers the oxygen levels that fish need to survive.

"I'd say the fish died from low oxygen levels, mostly because of the hot days and warm nights," Kilroy said.

Norton said he believes the deaths would have been greater had the Watersheds Authority not installed the aeration system and mixing fans.

The system was operating Sunday, Kilroy said.

"It had been in operation 27 of the last 72 hours," Kilroy said. #

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