The San Justo Reservoir, owned by USBR, is operated by SBCWD to provide agricultural and municipal/industrial water to its customers in San Benito County. Central Valley Project (CVP) water is delivered from the San Luis Reservoir, in Merced County, to Santa Clara and the City of Hollister and San Justo Reservoir via the Bifurcation Station located on Route 152. To keep water flowing through the system, water districts use reservoirs and water tanks for storage. One such water storage facility that the San Benito County Water District (SBCWD) utilizes is the San Justo Reservoir. It has a circumference of approximately 21,500 feet and its capacity at full 500-feet elevation is 10,308 acre-feet or 2.4 trillion gallons. The reservoir allows SBCWD to store water to ensure that the County has sufficient water during peak usage season between March and September.

While the U.S. Bureau of Reclamation (USBR) owns the San Justo Reservoir, SBCWD is the distributor of CVP water. SBCWD is responsible for keeping the water level at a certain elevation, which is adjusted seasonally; measuring input and output; and distributing water to and from the reservoir to its customers. In addition to the reservoir's role as a water storage facility, it was used for local recreation, picnicking, boating, and fishing.

In January 2008, zebra mussels were discovered in the San Justo Reservoir. Zebra mussels are an invasive species that attach themselves to hard substrate (the natural or man-made material that exists in a marine environment). Zebra mussels pose a significant threat to the reservoir’s ecology and SBCWD’s ability to effectively operate the reservoir (as the mussels can clog intake structures and pipelines). Zebra mussels have already infested the Hollister Conduit and Distribution System and, if not treated, could also spread to other water bodies. Consequently, the reservoir was immediately closed for public use. A treatment plan is being developed to be implemented around late 2011 or early 2012. The general public is being kept informed through public meetings, flyers, and other agency web sites. 

In an effort to control/eradicate the destructive aquatic mussel, SBCWD has partnered with federal, state, and local government agencies to plan an attack on the invasive species.

Zebra Mussels are a non-native invasive freshwater species that colonize on surfaces.
Larvae are microscopic and adults can grow to two-inches long and live for five years. Their shells generally have light and dark alternating stripes and an adult female can release up to a million eggs in a year. Read more about the Zebra Mussel by

clicking here.

Originating from Eastern Europe, zebra mussels have been spreading from the Great Lakes region to other parts of the United States over the last 20 years. The spread of zebra mussels usually occurs from activities such as boating and fishing. Zebra mussels can spread by attaching themselves to boat trailers, boat hulls, engines, props, and anchor chains. Its larvae can be carried in boat bilge water, live wells, bait buckets, and engine cooling systems. Once introduced into a new waterway, the mussels quickly reproduce.

Recreation Ban at San Justo Reservoir:
After the discovery of zebra mussels in 2008, USBR, SBCWD, SBC, and other concerned agencies had a meeting where it was decided to close the reservoir to all recreational uses while evaluating treatment options. Read more about ban by clicking here.

The introduction of one mussel could disturb the natural ecology, impede water system infrastructure, and disrupt recreational activities, costing the state and local water and recreation agencies millions of dollars annually in increased public education, monitoring, maintenance, containment, and eradication efforts. When zebra mussels invade our local waters they can clog water intake structures and pipelines, requiring routine treatment. This is problematic since we depend on a reliable water supply.

The discovery of the zebra mussel at San Justo Reservoir is particularly troubling because it is a link in the San Felipe Project. San Felipe is part of the U.S. Bureau of Reclamation’s massive statewide water distribution system, known as the Central Valley Project (CVP), and pipes link San Justo Reservoir to the entire network. The water network spreads across the Central Valley, into the Delta and north to the Cascade Range. The CVP is a critical water supply source for Californians in that it provides water for farming, drinking, industrial, recreational, and environmental uses.The zebra mussels must be eradicated to help ensure water conveyance to SBCWD customers and to restore the reservoir’s ecology and recreational activities. To achieve this, a variety of interrelated government agencies and districts are working to identify, develop, and implement the optimum eradication strategy.

Both the Bureau of Reclamation and SBCWD are involved in the eradication effort. Bureau of Reclamation's focus is the San Justo Reservoir. The SBCWD is eradicating zebra mussels from the point water leaves the reservoir—the water distribution system. Other agencies involved in the this effort include Santa Clara Valley Water District, California Department of Water Resources, California Department of Fish and Game, California Department of Boating and Waterways, and California State Parks.

Complete eradication is extremely difficult due to the tolerance and toughness of the zebra mussel. SBCWD and the Bureau of Reclamation are currently looking into aggressive measures to control, eradicate, and prevent the spread of the mussels into non-infested waters.

In an effort to help control the spread of the mussels into the extensive distribution system, SBCWD is developing treatment options to treat the system with known chemicals and treatment processes commonly used in treating infected water.

The eradication strategy will be determined following shoreline studies of the reservoir. The Bureau of Reclamation has lowered the water level so biologists can study the mussels attached to the bank. Samples are being tested to determine what treatments are most effective.

Links to maps displaying water district domain, project and site boundaries.


© 2009 San Benito County