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Invasive walleye keep popping up where they aren't supposed to be

A fisherman holds a walleye caught in Lake Cascade on May 7, 2022.
Idaho Department of Fish and Game
Mike Thomas
Angler holds up a walleye caught in Lake Cascade on May 7, 2022. This is the second illegally-stocked walleye confirmed to be caught out of Lake Cascade.

Five walleye have been found in southwest Idaho lakes and rivers this year - places they don’t belong.

On May 7, anglers, including an off-duty state Fish and Game employee, landed a 20-inch walleye in Lake Cascade, the second of its kind caught there since 2018.

On May 24, Fish and Game received its first-ever report of a walleye caught in Lake Lowell. Agency Southwest Fisheries Manager Art Butts said a second walleye was landed at Lake Lowell in late July, near the outlet.

“The Snake River is another thing,” he said. “We've had multiple fish caught in the Snake River this summer. That's very concerning.”

Anglers have hauled in walleye below the Swan Falls dam and near Melba, Butts said. Further upstream, the fish were first seen in the C.J. Strike Reservoir in 2008, and only occasionally since.

“This summer, it sure seems like things have really picked up,” Butts said.

Walleye are native to the midwest, where there are lots of other fish to satiate their voracious appetite. In Idaho and other parts of the west, river systems are simpler, Butts said, making it easier for the aggressive fish to crowd out other species.

He references Washington state’s Moses Lake, where walleye were introduced as a sport fish.

“It was a renowned crappie fishery in Moses Lake, and [the introduction of walleye] totally collapsed the crappie fishery,” he said, adding that the walleye there are now starving due to having decimated their own food chain.

Walleye could similarly threaten the bass and bluegill fishery in Lake Lowell, and perch and smallmouth bass in Lake Cascade.

The invasive fish has not been legally introduced in southwest Idaho. Butts said walleye surely had human help to get into Lake Lowell and likely other places where they’ve turned up by surprise. In the Snake River, the fish was likely introduced upstream more than a decade ago and has migrated.

“It's especially concerning having walleye in the Snake River system because further downstream you have the likelihood of these fish starting to interact with salmon and steelhead smolts,” he said.

Surveys by Idaho Fish and Game this summer attempting to find more walleye have been unsuccessful in Lake Lowell and Lake Cascade, but the agency plans to continue those efforts to try and understand the size and origin of the walleye population.

The agency wants anglers to report walleye and turn the head over for testing. A marketing campaign with signage is planned to start this fall.

Mineral content in the fish’s inner ear can establish its origin when compared with other native fish. Tests on the walleye found in Lake Cascade have yet to be completed.

If necessary, more aggressive removal programs could be established, similar to what already exists on north Idaho’s Lake Pend Oreille.

Walleye were illegally introduced into that water system in the 1990s. Fish and Game netthe lake each spring to try and reduce the population and heavily promotes walleye fishing at Lake Pend Oreille, including offering $1,000 reward for anglers who catch one of 100 electronically tagged fish.

Ramping up surveys and mitigation efforts in southwest Idaho, Butts said, will take resources away from other projects but are important to do now.

“It's almost impossible to put the genie back in the bottle once these fish get established.”

Troy Oppie is a reporter and local host of 'All Things Considered' for Boise State Public Radio News.

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