Bear Gulch Reservoir hides in plain sight in Atherton, providing water for local residents

by Linda Hubbard on May 7, 2013

Get off the beaten path a bit, and you’re apt to discover something hiding in plain sight, something actually pretty big. Case in point, the 166 million gallon (at capacity) Bear Gulch Reservoir in Atherton, a body of water much more visible on Google Earth than to area residents.

We paid the Reservoir a visit and chatted with three California Water Service Co. employees who are involved with  its operation — Dawn Smithson, Tony Carrasco and John Gomez (pictured left to right in front of the valve house). Along the way we picked up some facts that we think may be as surprising to people as the reservoir’s existence:

  • When residents of Menlo Park, Atherton, Portola Valley and Woodside turn on their tap, the water that pours out is from Bear Gulch about 20% of the time on an annual basis, with the other 80% coming form Hetch Hetchy. “We treat our local supply of water,” says Tony. “Not a lot of customers know that we have a treatment plant here.”
  • The reservoir is filled from Santa Cruz Mountain rain water run off. The Woodside Diversion Dam, which was built around 1840 as a grist mill and is located within the 1,200-plus acre California Water Service Co. watershed, is one source; the second source is water diverted from the lower portion of Bear Gulch Creek near Manzanita Rd. in Woodside.
  • The California Water Service purchased the Bear Gulch Water Co. from the University of California in 1936. Precessor water companies include Arroyo de La Presa (1863), Corte Madera Water Co. (1863-1873), Menlo Park Water Company (1873-1889) and Bear Gulch Water Company (1889-1936).
  • Bass are easily spotted swimming in the reservoir, but fishing — as well as visits (otherwise known as trespassing) — is not allowed, except for once a year. That’s when the Bear Gulch District hosts children from Ronald McDonald House in Palo Also for a day of fishing and picnicking. “But it’s really more than just fishing,” added Dawn. “The Menlo Park fire department is also here along with their equipment. It’s a day where the kids can feel like healthy kids.”
  • When it was opened, the capacity of the reservoir was 122 million gallons. That increased, at one time, to 215 million. Now, it’s 166 million. “When it reaches 50 million, which is the emergency base, we stop production and shut down the filtration plant,” said John.
  • The name of of reservoir dates from 1850 when James H. Ryder was working for Dr. Robert Orville Tripp’s lumber company, which used oxen to haul the logs to what is now Redwood City, where they were then floated to San Francisco. When two oxen went missing, Ryder went looking for them only to be attached by a grizzly bear with two cubs when he stopped for a drink at a creek. Severely mauled, he survived — and the creek became known as Bear Gulch Creek.

Photo by Scott R. Kline


Gail Siri March 28, 2016 at 12:03 pm

What is going on at the Reservoir? Many trucks going in (loaded) and dumping dirt on the property. This has been going on for a number of weeks.

PaulT May 11, 2017 at 9:10 pm


As per the recent NBC Bay Area News report, the City of Atherton is listed as one of the San Mateo County cities where the water source has 1,2,3 TCP contamination. The contaminated system is identifed as the Bear Gulch Water Treatment Plant.

More info below:

And here is the detail spreadsheet listing the contaminated systems:

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