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A fishy mystery: Why is the Willamette River seeing record numbers of coho salmon?

A fish swims through murky water.
Oregon Department of Fish and Wildlife
This is one of the first coho salmon to go through the fish ladder at Leaburg Dam in 2023.

It’s a great time to go fishing in Western Oregon. But recent runs of coho salmon have set a record … and … spawned a mystery.

Jeff Ziller is the district fish biologist for the South Willamette watershed with the Oregon Department of Fish and Wildlife. He said coho haven’t been stocked on the Willamette River since the 1990s. Yet, in the 2000s, wild coho started showing up there. Last year set a record with close to 30,000 fish, and coho were found above the Leaburg Dam for the first time ever.

“We don't know why they started coming back, but they evidently have found some good habitat up here,” Ziller told KLCC.

So far this year, more than 40,000 coho have come over Willamette Falls, and are making their way upriver. Some will make it to the Eugene / Springfield area.

Ziller said coho fishing is open on the McKenzie below Leaburg, and the Middle Fork and Coast Fork of the Willamette, just in case. “We don't know how many fish are gonna come up here," he said. "It could be zero, it could be several thousand.”

The fish are not native to the upper Willamette River. Salmon generally return to the waters where they were born. But, Ziller said, about 5% will travel to locations that haven’t been colonized in the past. He said it’s a great survival tactic, and the reason why coho are being seen in unfamiliar waters.

Anglers can check out the current Oregon fishing regulation updates for details about how and when to fish for coho.

Karen Richards joined KLCC as a volunteer reporter in 2012, and became a freelance reporter at the station in 2015. In addition to news reporting, she’s contributed to several feature series for the station, earning multiple awards for her reporting.