A fish-stocking truck will back down the Diamond Lake Resort boat ramp Thursday and the assembled crowds will cheer as the first 6,000 rainbow trout burst from it and into the freshly chub-less Diamond Lake.

A fish-stocking truck will back down the Diamond Lake Resort boat ramp Thursday and the assembled crowds will cheer as the first 6,000 rainbow trout burst from it and into the freshly chub-less Diamond Lake.

Jim Muck will be standing by, with his attention focused just as much on the truck's wheel wells as the fish.

He knows the Oregon Department of Fish and Wildlife's truck was washed before it set off to the Cascade Crest to release those trout.

But what about the trucks, boats and trailers that will hit the water here during Saturday's opening day of the 2007 trout season?

Are they bringing some other new invader to the lake?

"Diamond Lake is a clean lake, and we need to keep things from getting into the lake," says Muck, an ODFW fish biologist in Roseburg.

The fear of a new introduction of invasive species here has prompted several state and federal agencies to begin teaching Oregon boaters how to reduce the risk that aquatic pests will hitchhike on boats and trailers to uninfected waterways.

This time, they're not talking illegal fish-stocking.

Forget the odds that some schmuck might show up here this spring with live tui chubs to use as bait — like someone did 20 years ago and almost ruined Diamond Lake for good.

That same guy's boat hull might have zebra mussels that could take hold and overrun the lake. His live-well could contain tiny New Zealand mud snails that could kill the lake's plankton just as the chubs did. His trailer could have a hydrilla sprout. Or, gulp, a quagga.

Any one of them could ruin Diamond Lake like tui chubs did, should they show up as accidental tourists.

"We know exactly where invasive species are spread — boat ramps," Muck says. "We need to stop invasive species there, before they get into the lake."

So a new mantra will begin echoing from beneath Mount Thielsen, and eventually it will reach more than 100,000 boat-owners statewide: Wash your boat.

Get rid of any critters stuck to your boat every time you pull it out of a river or lake. Wash the hulls, disinfect the live wells and power-wash that trailer. Let it air-dry five days before heading up.

The fishing spot you save might be your own.

"We're going to use Diamond Lake as the poster child to teach boaters a common practice on how not to carry invasive species from one water body to another," Muck says. "We want people to wash their boats before they head up the hill.

"It only takes one boat to transfer an invasive species," Muck says. "That's why we need to wash all the boats."

Though the individual risk of carrying an aquatic hitchhiker is low, the stakes are high.

Some invasive species can thrive in non-native waters because they are safe from predators or diseases seen in their native habitat. Like chubs, they can reproduce exponentially and out-compete native fish for food and space.

Diamond Lake's chubs over-ran stocked rainbows and triggered toxic algae blooms before they were killed with rotenone last September. The lake was restocked this week in what amounts to the equivalent of a huge fishing mulligan.

Invading mussels can do all that and more. The mussels filter zooplankton, altering the ecosystem much like the chubs did. But they also can ruin boat engines, jam steering equipment or cloak the lake in a mat of hydrilla.

The New Zealand mud snail already is in the lower Umpqua. Muck wants to keep it out of the upper basin, including Diamond Lake.

Another fear is quagga, a nasty mussel discovered in January in Lake Mead in Nevada.

The most likely accidental carrier is an out-of-state boat, Muck says. But many of these species can hitchhike on practically anything.

"No one's doing this deliberately," says Leah Miller, director of watershed programs for the Izaak Walton League, which joined a national campaign to curb the spread of invasive aquatic species.

"People just don't realize they can live on your boot or even in your dog's fur," Miller says.

Those that show up at Diamond Lake will be stopped before they reach the boat ramp. They'll be asked to drive up to the nearby Texaco station, where a portable pressure-washer will be available for a free washing.

"We're going to be a presence at Diamond Lake, trying to identify the at-risk boats, send them up the hill and get them washed," Muck says.

In the Great Lakes region alone, at least 184 aquatic invasive species are already established, Miller says.

Already, Americans spend $9 billion a year battling invasives.

And just six quarters at a self-serve car wash can keep them from expanding here.

"Definitely, prevention is the best way to go," Miller says. "It's the least expensive and easier way."

Reach reporter Mark Freeman at 776-4470, or e-mail mfreeman@mailtribune.com.