Park workers found several hundred dead fish floating on Lake Balboa in the Sepulveda Dam Recreation Area early Wednesday, apparently killed after oxygen flow to the man-made lake was accidentally disrupted.
The dead fish, including trout and catfish planted in the lake last winter and this spring, had to be scooped from the water by parks employees in boats.
Dick Ginevan, chief city recreation and park supervisor for the valley region, said the fish apparently suffocated during the night when the Donald C. Tillman Reclamation Plant was temporarily shut down for construction.
Each day, the Tillman plant pumps an average of about 20 million gallons of reclaimed waste water into year-old Lake Balboa. It is the sole source of fresh water to the lake, said plant manager Bob Birk.
The plant was shut down for about four hours late Tuesday, said Sam Furuta, assistant director of the city's Bureau of Sanitation. Birk said the shutdown, announced ahead of time to lake managers, was necessary to allow the plant to switch over to a newly completed discharge pipe.
Parks officials mistakenly thought that the lake's built-in aeration system would keep oxygen levels sufficiently high during the shutdown, despite the lack of fresh water, Ginevan said.
"We haven't had a fish kill all summer, but things break down, things happen," Ginevan said. "It's a learning process for us. We are dealing here with nature." Bob Hayes, public information director for the city Board of Public Works, said the plant shutdown was unavoidable for safety reasons.
"I can appreciate the fact that fish died, but if we didn't do what we had to do, we'd be in violation of all sorts of federal and state regulations," he said.
Public works and parks officials are scheduled to meet today to discuss the mishap, said Eric Rose, spokesman for City Councilwoman Laura Chick.
Meanwhile, Ginevan said the Parks Department plans to continue planting fish in the lake. So far about 14,000 trout, 20,000 catfish and about 500 blue gill have been released there.