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Walleye a Growing Threat to Snake River Salmonids by Staff Columbia Basin Bulletin, October 26, 2026

Eat Smolts In The Spring,
Feed On Other Non-Natives Rest Of Year

A fish introduced to Lake Roosevelt over 60 years ago has become the darling of some Northwest anglers, but also a growing predatory threat to salmon and steelhead smolts in the Snake River, according to state and tribal fisheries biologists speaking at the Northwest Power and Conservation Council's October meeting.

Walleye soon migrated out of Lake Roosevelt and down into the lower Columbia River. Over the past decade the fish has rapidly expanded its range into the Snake River and is now common upstream of Lower Granite Dam in the stretch of the Snake up to Hells Canyon Dam. They are also found in the Tucannon and Walla Walla rivers downstream of Lower Granite, and in the Clearwater and Salmon rivers upstream of Lower Granite.

Walleye, an opportunistic predator, devour several water species over a year of voracious feeding, according to Andrew Murdoch, a biologist with the Washington Department of Fish and Wildlife, and Jonathan Armstrong of Oregon State University, and others.

In their recent study that took monthly stomach samples from walleye in the lower Snake River, they found that walleyes' appetite includes native lamprey, and salmon and steelhead smolts during the spring months of April, May and June. Their diet in late summer and fall, August through November, consists of non-native shad and Siberian prawns. In December, the fish feast on native northern pikeminnow.

In essence, the scientists found that walleye prey on native species in the spring and non-native species during most of the remaining year, and it's those non-native species found in the Snake River that are supporting walleye's rapid population growth in the river. It is a phenomenon they call invasional meltdown hypothesis, which is how the introduction of one or more non-native species make it easier for other non-native species to establish and thrive, leading to a cascade of invasions and a decline in native biodiversity.

For comparison, the upper Columbia River walleye population is low and stable, Murdoch said. That is due to the fact that there are no shad and no Siberian prawns that support walleye when salmonids are not available.

The study, "Complementary prey phenologies enhance invasional meltdown: a case study in the Columbia River Basin," was published April 4, 2026 as an Open Access study in the journal Biological Invasions. Co-authors are Murdoch, Jonathan Armstrong of Oregon State University, Matt Polacek from WDFW and Rochelle Polacek, also from WDFW.

--See CBB, June 8, 2026, "Lower Snake Walleye Study Shows How Invasive Predator Fish Benefit From Other Invasive Species (Siberian Prawn, Shad) For Food,".

Although Oregon, Washington and Idaho all consider walleye a sports fish, biologists are worried about their impact on native species. So, the states adopted a policy that "considers walleye in the Snake River from the mouth to Hells Canyon Dam as an incompatible species with native salmonids. The presence of walleye within this reach compromises salmon and steelhead recovery."

The policy statement was declared by the Snake River Basin Non-Native Piscivore Workgroup, a committee of fisheries scientists from tribes and the states of Oregon, Washington and Idaho.

In response to the policy, the three States plan research and management actions aimed at reducing the walleye population. And, to help support these efforts, the states are encouraging anglers to harvest all the walleye they catch.

There is a lot that scientists don't know about walleye. According to the Council's Oct. 6, 2026 Memorandum (2026_10_f3.pdf), little is known about walleye abundance and population trends, their distribution, their movement and where they spawn. Also, more needs to be known about size, timing and location of predation impacts, food web and predator-prey dynamics and the feasibility and effectiveness of management actions.

"Regional fish and wildlife managers are already collaborating to improve this understanding through monitoring, research, tagging, and other efforts through an informal Walleye Workgroup," the memo says.

What is known is that walleye can be found mostly near the bottom of rivers, but at times will suspend in the water column. They can survive higher temperatures than salmon and steelhead, including temperatures as high as 32 degrees Centigrade (90 degrees Fahrenheit), although they prefer temperatures of 20 to 25 C (68 to 77 F), according to Murdoch et al.

The fish are ambush predators using river currents and breaks to hold and feed and can eat other fish within as early as age 0, in the first year of life. Their greatest metabolic demand comes at the moderate water temperature of 22C (72F).

Walleye reproduce by spawning 20,000 to 30,000 eggs per pound of body weight (high fecundity) over gravel and cobble. The eggs hatch in just 7 to 25 days.

Other non-native species are also gaining in population in the Snake River, according to Grant Waltz, who manages the Bonneville Power Administration-funded Northern Pikeminnow Management Program at the Oregon Department of Fish and Wildlife. Northern pikeminnow are a native species that, among other foods, feed on juvenile salmon and steelhead. However, through the Management Program their population is in decline. Removing 10 to 20 percent of the fish over 11 inches per year has reduced the fishes' predation on salmonids by 40 percent, Waltz said at the Council meeting.

In the Little Goose Dam's reservoir, as pikeminnow have been in decline, smallmouth bass, a non-native species, and walleye populations have been rising, with "notable" increases of walleye in the mid-reservoir, Waltz said.

In the Lower Granite Dam reservoir, there is a very low abundance of Northern pikeminnow (a steep decline in population since 1991), but a steep increase in smallmouth bass. Walleye population size has risen slightly since they were first detected.

There is a general decline of Northern Pikeminnow in the John Day Dam reservoir, but a long-term increase in smallmouth bass and a notable increase in walleye, Waltz said.

In her presentation to the Council, Marika Dobos of the Idaho Department of Fish and Wildlife, showed a steep increase in the number of walleye trapped at the Lower Granite Dam fish trap from 2016 through 2026.

She said that the data collected show an increase in abundance and the spatial expansion of walleye in the lower Snake River and tributaries, at the same time that juvenile salmon and steelhead are declining in numbers.

Related Pages:
Walleye Willie Shootout Returns by Staff, Columbia Gorge News, 5/20/25
Walleye Continue to Move Upstream, Pose Threat to Native Salmon and Steelhead by Staff, Lewiston Tribune, 10/24/24
Catch, Kill, Report Walleye in Idaho's Salmon and Steelhead Rivers by Andy Walgamott, Northwest Sportsman, 3/29/24
Invasive Walleye Moving Higher into Snake River Basin, Threatening Juvenile Salmon, Steelhead, Lamprey by Andy Walgamott, Columbia Basin Bulletin, 3/22/24
'Not Good for Salmon and Steelhead': Smolt-Eating Walleye Worry Fishery Managers by Eric Barker, Spokesman-Review, 8/30/23
Increasing Number of Predatory Walleye Logged at Lower Granite Dam by Nolan Smith, Big Country News, 6/29/15
WDFW Removes Bag Limits for Bass, Walleye, Catfish on Columbia River, Tributaries to Protect Salmon by Andy Walgamott, Columbia Basin Bulletin, 3/4/16
New Rules Mean More Walleye, Fewer Sturgeon for Washington Anglers by Eric Barker, The Bend Bulletin, 3/13/13
It's Official: Bag Limits Off in WA for Columbia/Snake Bass, Walleye, Channel Catfish by Andy Walgamott, Columbia Basin Bulletin, 3/3/13
Bass, Walleye Pose Substantial Threat To Salmonids by Andy Walgamott, Columbia Basin Bulletin, 3/6/9
Pikeminnow Season Catch Up; Data Confirms Snake Walleye Increase by Andy Walgamott, Northwest Sportsman, 10/13/22

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