By Staff Report

A biologist from the California Fish and Game commission surfaces from the water after diving into San Justo Reservoir to check for zebra mussels.

The invasive zebra mussels sit in a wheel well of a boat that was pulled out of the San Justo Reservoir.

Sean Hoobler, left, and Diane Haas, biologists for the California Fish and Game Commission, plan out their first dive into the San Justo Reservoir.

Fish and Game dive into San Justo

The effects of heavy January rains have slowed efforts to determine the extent of an infestation by a rapidly proliferating non-native mussel found in a San Benito County reservoir earlier this year.

When biologists from the state Department of Fish and Game descended into the murky waters of San Justo Reservoir last week, they found large clumps of the fingernail-size zebra mussel around dock structures. But with visibility limited to an estimated 6 inches, a more comprehensive survey of the lake off Union Road west of Hollister will have to wait.

The mussels arrived, probably from Russia, at the Great Lakes in the late 1980s. They have since become a multi-billion dollar headache, clogging pipes and equipment and sweeping the waters clean of native life.

When the presence of mussels was confirmed at San Justo Reservoir the week of Jan. 14, state officials expressed fear that the infestation might be more widespread. Should the mussels be discovered in the Central Valley Water Project system, the consequences could be devastating.

"That's the big sweat we're having right there," said Harry Morse of DFG.

Divers were scheduled to check a key link in that system this week, with a team entering O'Neill Forebay near Santa Nella. But light rains forced them to stall the dive.

Surveys in parts of the system closer to San Justo failed to turn up any mussels, Morse said.

If the infestation is confined to San Justo, biologists from DFG will next have to determine how to eliminate the mussels. That decision is expected to take some time.

The discovery of zebra mussels locally was the first in California. A close relative, the quagga mussel, has been found in the state, and poses a similar threat.

Until biologists figure out how to proceed, San Justo, a popular spot for fishing, picnics and boating, remains closed to the public.