Treatment plant off hook in fish deaths, official says

FREMONT — A combination of above-average algae growth and urban runoff from the first storm of the season appears to have caused the deaths of thousands of fish earlier this month in a section of Alameda Creek, said Paul Piraino, general manager of the Alameda County Water District.

A leak from an upstream wastewater treatment plant does not appear to have contributed to the incident, which was the largest reported fish kill in the creek in more than two decades.

Test results showed low levels of toxicity in the water, which led officials to conclude that the leak from the wastewater facility did not contribute to the fish kill.

Approximately 5,000 fish were found belly up Oct. 6 in a 150-acre-foot section of the creek spanning from just east of Mission Boulevard in Fremont to a rubber dam about 1,200 feet to the west.

In preparation for rain this weekend, water district workers on Tuesday lowered the dam to drain the area of water, thereby killing some of the algae, Piraino said.

Water district officials said they do not expect this weekend's predicted showers to cause a second fish kill because algae levels should be lower, and because the second storm of the season usually carries less runoff of organic materials into the creek.

The district announced its findings after consulting with experts specializing in urban runoff, fisheries and stream beds, Piraino said.

Several factors appear to have caused oxygen levels to plunge in the affected area, effectively suffocating the fish. The build-up of algae on the bottom and sides of the creek drew oxygen at night when there was no sunlight for photosynthesis, Piraino said. Meanwhile, the first storm of the season brought cloudy, poorly oxygenated water into the creek that carried with it runoff of organic materials such as animal waste, which also sucks oxygen from the water.

With less sunlight for photosynthesis, and more oxygen-consuming materials in the water, levels of dissolved oxygen dropped from about 11 parts per million the prior week to less than 1 part per million on the day of the fish kill.

"It sounds like what happened on Oct. 6 is we had a perfect storm," Piraino said...

...Read full article at the Fremont Argus.