A fingernail-sized mollusk is quickly becoming one of California’s more worrisome invasive species.

Since quagga mussels showed up in a Southern California lake last January, experts have forecasted their spread through the state. For now, quaggas have stayed out of Monterey County– but cash-strapped local officials are doing next to nothing to keep them out.

The mussel migrates in two ways: by floating through waterways and pipes, and by hitching rides on nets and boats. “Where the water goes, they go,” says Andrew Cohen, who chairs the state’s scientific advisory panel on the threat.

Quagga larvae have traveled from the Lake Mead reservoir southeast of Las Vegas to the Lake Havasu reservoir on the California-Arizona border, Cohen says. From there, they’ve spread to the water district that serves San Diego and Orange counties, rearing their clammy heads in roughly 15 reservoirs.

Experts believe that a waterway’s pH, salinity, temperature, and oxygen and calcium levels are factors in its vulnerability to a quagga invasion. High-risk water bodies in Monterey County include the Pajaro, Salinas, Carmel and Arroyo Seco rivers, Cohen says.

The invasive zebra mussel– quaggas’ annoying cousin– appeared in the Great Lakes more than 20 years ago. Growing deeper on softer sediments, the quaggas waged a slower but more effective takeover, eventually crowding and wreaking havoc on native wildlife. “As bad as the zebra mussels were, the quaggas were worse,” Cohen says.

Both likely traveled thousands of miles overland on boat equipment.

“It’s clear they can travel over great distances,” Cohen says, noting that quaggas have been found clinging to boats at check stations throughout the state. (There are no check stations in Monterey County.)

Once the mussels’ larvae have invaded waterways, they suck up nutrients and take over habitats, with potentially disastrous impacts on native fish and the animals that eat them.

The mussels are notoriously hard to eradicate once they become established. Ozone, irradiation and other treatments have shown some capacity to destroy the invaders, but at potentially significant environmental costs.

So far the marauding mussels have spared Monterey County. But experts fear that an infestation in Northern California could infiltrate the State Water Project pipelines, which deliver water to more than 20 million people.

Salinas Valley agriculture draws water from the ground, which may keep mussel larvae out of local irrigation pipes. And Monterey County is independent of state and federal water projects.

For now, local officials are keeping the mussels at the periphery of their radar.

“We do not have a boat inspection program, nor does San Luis Obispo County for Lake Nacimiento,” says Bill Phillips, deputy general manager of the Monterey County Water Resource Agency. “We don’t have the ability to inspect every single boat, inner tube or wetsuit that goes into a lake.”

The agency has installed mussel-monitoring stations in San Antonio and Nacimiento lakes, he says. In the meantime, officials are trying to assess the potential threat.

The worst-case scenario would be if the mussels hitched a ride into the rubber dam that’s under construction in the Salinas River, part of the Salinas Valley Water Project. “The alarmist view is that the same thing would happen as with the Great Lakes area,” Phillips says.

Researchers think quaggas prefer waters with a threshold level of calcium– which could spare the low-calcium Lake Nacimiento. But there are no guarantees quaggas won’t colonize it.

Otto Schmidt, who lives near the upper Salinas River, sees the quagga as a sort of doomsday clam that could hitch a ride from Lake Nacimiento to the Salinas River, ultimately destroying agricultural infrastructure.

He’s horrified that Monterey County does not have checkpoints to inspect boats for the invader, while counties to the south have protocols in place for preventing its spread. “We gotta be proactive, not reactive,” he says.