Erik Oeverndiek/Daily Journal San Francisco utility officials are probing a breach in a metal pipe in San Mateo on Saturday that sent thousands of gallons of treated drinking water into San Mateo Creek and killed more than 100 fish.

Dozens of fish were killed after a pipe burst Saturday afternoon sending gallons of drinking water disinfected with chloramine into San Mateo Creek.

The San Francisco Public Utilities Commission was alerted to the leak at about 4 p.m. Saturday. What caused the 60-inch water main to break is not yet known but crews are working to fix the problem, said Steven Ritchie, assistant general manager for water at the commission. In the meantime, crews are working to divert water from entering the creek while also trying to prevent the chemicals from harming the creek by diluting the water, said Ritchie. Water was still being released Tuesday while a fix was being worked on by crews.

"It’s unfortunate circumstances,” Ritchie said of the fish.

Acute toxicity caused the death of about 100 fish including rare steelhead. Ritchie said the water is disinfected so it’s safe for drinking but the chemicals, unfortunately, have negative impacts on wildlife. Chloramine is a combination of chlorine and ammonia.

San Mateo Creek, on the border of San Mateo and Hillsborough at stretches, flows about five miles from the Crystal Springs Reservoir to the Bay. Water leaked into the creek is from the Hetch Hetchy system. Water from Crystal Springs was used to dilute the water and save some wildlife.

Once it burst, the pipe sent water out at 1,000 gallons per minute down a hillside into the creek. Crews were able to slow that to about 100 gallons per minute while work was being done this weekend.

Ritchie said the 1932-era pipe that broke was likely corroded, but the official cause of the burst is not yet known. The piece of pipe was previously identified as needing to be replaced. Ritchie does not believe this will cause a long-term environmental problem.  

Representatives from Hillsborough and San Mateo both said the cities did not have any significant negative impacts as a result of the break.

State Department of Fish and Wildlife and the Regional Water Quality Control Board are investigating the incident and could assess penalties for the fish killed and any environmental damage.

The Regional Water Quality Control Board has issued penalties previously for potable water discharges throughout the Bay Area. For example, In May 2011, Caltrans was removing a beam on the north side of Bear Creek Gulch in Woodside that resulted in a crack in the nearby water pipe. As a result, 11,000 gallons of potable water containing chloramine was released into the creek, which contributed to the death of many fish in the water. Caltrans faced a $31,250 fine for the incident.

In 2007 and 2009, water discharged into Polhemus Creek in San Mateo also resulted in the death of steelhead fish. A $200,000 fine was issued as a result.

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