Invasive mussels the size of fingernails that clog pipes, spoil beaches and crowd out native aquatic life are lurking at Idaho's border, and if they spread to the state's waterways they could cost $91 million annually, experts warn.

But the costs of fighting the invasion likely will keep the state from doing what pretty much everyone involved acknowledges would be a good idea - keep the mussels out of Idaho.

Idaho Department of Agriculture Director Celia Gould told budget writers earlier this month the multimillion-dollar cost of keeping quagga and zebra mussels out of the state was too high in the current state of the economy.

But Republican Rep. Eric Anderson of Priest Lake - who has campaigned against invasive species his entire legislative career - told the Legislature's Environmental Common Sense Task Force Thursday that the price of invasion is too high for the state to do nothing.

"I believe we'll find mussels here if we don't do something this spring," Anderson said.

The mussels were inadvertently introduced into the Great Lakes in the mid-1980s, and they have spread throughout the East and Midwest. In 2007 they were found in Lake Mead on the Nevada-Arizona border and have since spread into California, Colorado and Utah.

California has been forced to close some lakes to prevent the spread of the bivalves. They reproduce and spread rapidly, clogging machinery and water pipes and destroying aquatic ecosystems. Once established, they're nearly impossible to eradicate.

Idaho's extensive irrigation canals and ditches are among the most threatened systems, along with its hydroelectric dams, fish hatcheries, marinas and drinking water systems.

Every boat that comes into the state needs to be washed before it is allowed in state waters in order to keep the mussels out, officials said. That requires up to 125 washing stations at an estimated cost of $150,000 a piece, a vendor reported.

Anderson proposed that the owner of any boat used in Idaho be required to buy a $20 sticker to cover the cost of an extensive boat washing program. Mountain Home GOP Sen. Tim Corder said the state should consider even more drastic measures like quarantining lakes until a boat washing network is established at the borders and at larger lakes.

"We haven't convinced enough people how serious it is," Corder said.

The costs as well as the chance of failure have kept the state from moving on the issue so far. Republican Senate Pro Tem Robert Geddes, who sat through Thursday's meeting, expressed pessimism afterward.

Already a boat from Lake Mead was found in Bear Lake in southeast Idaho, and a lake a few miles away in northeast Utah was already infested with the mussels. Fish from Lake Mead were stocked in a reservoir on the Owyhee River just before the lake's own mussel invasion was known, state agriculture officials said.

The microscopic larvae can be carried into the state by the flows of the Snake River from Wyoming, by the Clark's Fork from Montana and even by waterfowl.

It will be hard to keep them at bay.

"It sounds impossible," Geddes said.

But Kurt Zeile, a representative of the Michigan company that sells boat washers, said the cost of keeping the mussels out is far less than the cost of dealing with them once they are here.

"I was in Kansas before they had zebra mussels, and I was in Oklahoma before they had zebra mussels," he said. "In each state they said they couldn't afford to wash boats."

Rocky Barker: 377-6484