Ten years ago, 12 adult coho returned past Rock Island Dam near Wenatchee, Washington. This year, 19,805 passed the dam. Returns past McNary Dam near Hermiston, Oregon, climbed from 4736 coho a decade ago to 33,385 this year – by far the most since counting began at the dam in 1954.

The rise in adult coho returning past seven or more mainstem Columbia dams to spawn this winter in upriver tributaries exceeds all expectations, said Tom Scribner, the Yakama Nation’s project leader. While most of the returning fish came from hatcheries, an expanding share comes from natural spawning that biologists hope will resurrect self-sustaining wild stocks.

The return of spawning coho to the upper Columbia reflects the success of a pioneering reintroduction strategy that no one had attempted before. The program is funded by BPA, Chelan County Public Utility District, Grant County Public Utility District and NOAA-Fisheries.

Biologists began rekindling the upriver runs in the 1990s with hatchery-bred fish from the lower Columbia, since no local coho adapted to the upper Columbia were left. Some wondered whether lower river fish, after many generations in hatcheries, could rebuild runs that would have to migrate hundreds of miles farther up the Columbia, past several major dams.

“There was a question whether it was really possible to do this so far above the dams,” said Roy Beaty, BPA’s project manager for upper Columbia coho restoration. “We really didn’t know whether the fish could swim that far.”

Irrigation diversions and development wiped out some 90% of native coho from the middle and upper Columbia during the late 1800s. A remnant population hung on but largely vanished by about 1980. Upriver coho did not receive protection under the Endangered Species Act, since none were left to protect.

BPA now funds the coho restoration program through the Columbia River Fish Accords and is completing an environmental impact statement assessing the construction and long-term operation of program facilities.