SAN MATEO -- The San Francisco Public Utilities Commission is still tallying the damage after a water transmission pipeline broke over the weekend, releasing chlorine-treated water into San Mateo Creek and killing dozens of fish.
SFPUC spokeswoman Alison Kastama said 200 or more fish died from exposure to the water, possibly including federally threatened steelhead trout. The agency is working to determine exactly why the 5-foot-diameter pipe burst and how many and what kind of fish died.
"It is most likely corrosion due to age," Kastama said regarding the cause of the break, which was reported around 4 p.m. Saturday by a homeowner on Crystal Springs Road along the San Mateo-Hillsborough border. SFPUC workers were able to slow the flow of water from the broken, roughly 80-year-old pipe within a few hours and stopped it completely by Tuesday.
The pipe was carrying water treated with chloramine, a combination of chlorine and ammonia, to customers in San Mateo County and San Francisco. The SFPUC manages the Hetch Hetchy Regional Water System, providing drinking water to about 2.6 million customers in the Bay Area.
Like most other metropolitan water agencies, the SFPUC treats its drinking water to destroy bacteria and parasites. SFPUC water -- which contains 1-2 parts per million of chloramine, according to Kastama -- is considered safe for consumption by people as well as mammals and birds, but is toxic to fish.
The California Department of Fish and Wildlife and the National Marine Fisheries Service are investigating the spill, which could result in penalties. National Marine Fisheries Service spokesman Jim Milbury said the agency has an unspecified number of investigations already open into previous leaks of treated water by the SFPUC.
Contact Aaron Kinney at 650-348-4357. Follow him at Twitter.com/kinneytimes.