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Water District Investigates Threat of Invasive Mussels

Contact: Susan Siravo
Office: (408) 265-2607, ext. 2290
Mobile: (408) 398-0754

Jan. 8, 2008

SAN JOSE — The Santa Clara Valley Water District is taking aggressive steps to determine if the invasive species, zebra mussel, is in any of its reservoirs, creeks or other water delivery systems.

The action follows the discovery of zebra mussels in San Justo Reservoir, which is in neighboring San Benito County. San Justo Reservoir receives its water from San Luis Reservoir, which is also one of the water district’s main sources for imported water.

Zebra mussel is an invasive shellfish that can clog water pumps and pipes and could potentially wreck havoc on the state’s water system. The shellfish are commonly transported between reservoirs by recreational boats. Bay Area boaters often frequent a number of reservoirs, which means the chance of the mussels spreading is significant.

“The spread of both quagga mussels and zebra mussels have created enormous problems in other parts of the country. We know that early intervention is the most effective strategy in controlling the mussels,” said water district board chair Rosemary Kamei. “That’s why we’re taking proactive steps now to find out if they are in any of our reservoirs.”

In the wake of the latest development, the water district is in the process of taking the following actions:

The water district is aiding California Department of Fish and Game (DFG) and the Department of Water Resources (DWR) in assessing whether the zebra mussels at San Justo Reservoir originated in San Luis Reservoir. The water district is inspecting its intake facilities in San Luis Reservoir. It is also working with DFG to perform subsurface inspections of its local reservoirs.

Test plates will be installed at Calero and Anderson reservoirs and at the intake facilities at San Luis Reservoir. The test plates are a Plexiglas substrate that is commonly used to detect colonies of zebra or quagga mussels. The plates will remain in the reservoirs for at least a month before any conclusions can be made.

As a precaution, the water district has temporarily ceased bringing water from San Luis Reservoir into Calero and Anderson reservoirs.

Background On Jan. 9, 2008, DWR confirmed that zebra mussels were discovered in the San Justo Reservoir on Jan. 8. This was the first confirmation of a zebra mussel population in a California reservoir. Zebra mussels are closely related to quagga mussels which have been creating significant clogging issues in southern California water systems since early last year.

For more information regarding zebra mussels visit DFG website at

The Santa Clara Valley Water District manages wholesale drinking water resources and provides stewardship for the county's watersheds, including 10 reservoirs, hundreds of miles of streams and groundwater basins. The water district also provides flood protection throughout Santa Clara County.