Diamond Lake boaters can expect a little quizzing about their boating habits from resort workers and campground hosts who are being recruited as part of a frontline defense against lake invaders.

Diamond Lake boaters can expect a little quizzing about their boating habits from resort workers and campground hosts who are being recruited as part of a frontline defense against lake invaders.

Where have they boated before? Have they cleaned their boat since then? Where are they headed next? are likely inquiries visitors will hear from Diamond Lake's regulars this summer.

The inquiries are part of an effort to keep invasive plants and animals out of the lake, which was treated with rotenone last fall to kill off 90 million tui chubs.

State and federal managers are trying to keep ahead of the next threat to the lake's water quality and trout fishery by identifying and cleaning boats that could have an unnoticed hitchhiker before they hit the water.

"The goal is to find that one hot boat — a boat that may be carrying some critters like invasive plants, mussels or fish," said fisheries biologist Jim Muck of the Oregon Department of Fish and Wildlife, which is one of several partners in the effort.

"We could check a thousand boats and find nothing," Muck said. "But we need to find that one hot boat before it hits the water."

Visitors suspected of towing a hot boat will be steered toward a new portable pressure-washing system for a little pre-launch cleaning.

It's all part of an effort to keep Diamond Lake the poster boy for clean boating and not a repeater of its invasive-species history, which includes two rotenone treatments for chubs.

"Obviously, tui chubs are the big threat to Diamond Lake," said Randy Henry, policy and program coordinator for the Oregon State Marine Board. "That's the one with the track record. But there are a number of critters that can do ecological damage there."

Hydrilla, zebra mussels and New Zealand mud snails, for instance, are non-native species identified in the West that can move in and overrun a fishery much like chubs did here, Henry said.

Diamond Lake Resort workers, ODFW creel checkers and others will be trained on identifying these threats during a workshop Friday at the resort.

The training will run from 10 a.m. to 2 p.m. at the Diamond Lake Lodge, which is at the resort on the lake's north end.

"It's to help people who live and work and spend a lot of time at Diamond Lake to be the eyes and ears that help keep another infestation from happening," Henry said.

The free training is open to the public and there is space for about 50 people, Henry said. The workshop will focus on identifying zebra mussels and hydrilla as well as how people can approach boaters effectively, Henry said.

"A lot of it is knowing how to ask the friendly questions," Henry said.

Diamond Lake is awash in friendly faces these days. Thanks to an aggressive stocking schedule by the ODFW, the lake's growing number of visitors are experiencing the best fishing there since tui chubs were re-discovered in 1993.

"It was wonderful," says Dick Ray, a retired banker from Paradise, Calif., who last week sampled several of the 65,620 rainbows stocked there so far this spring.

"We caught a limit of fish both days and four or five trout in the 5-pound range," says Ray, 68, who fished with two fellow retirees. "The eagles were there. The ospreys were there. It was just nice."

Nice is an adjective Muck would like to keep around at Diamond Lake.

The stocked fish amount to the equivalent of a huge fishing mulligan, a do-over for anglers who Muck believes might not fare so well should an invader return to Diamond Lake.

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.

Zebra mussels filter zooplankton, altering the ecosystem much like the chubs did. But they also can ruin boat engines and jam steering equipment.,

Hydrilla can overrun open water and turn entire lakes into green mats.

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

The most likely accidental carrier is an out-of-state boat, especially one that has sat in an infected water for an extended period of time before getting shipped to a new waterway.

Muck wants to make sure his agency remains the only entity putting live critters into Diamond Lake.

"Even crayfish can be an invasive species," Muck says. "We have to keep our eyes out for everything."

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