To get there, they had to brave the rapids of the Snake River, where expedition members tipped boats, lost gear and were stunned by the abundance of salmon. The Snake Basin coho salmon was officially declared extinct in 1985.
Dams are the primary cause of their demise.
In the last decade of the 20th century, fewer than two dozen adult sockeye salmon made it upstream past Lower Granite Dam, the uppermost Snake River dam with fish passage, to reach their spawning grounds in central Idaho. Of the scores of big dams in the Columbia watershed, the most deadly to salmon are the four federal projects on the Lower Snake River, located between Lewiston, Idaho, and the confluence with the Columbia River at Pasco, Washington. Biologists blame these four dams, in combination with four lower Columbia River dams, for at least 80 percent of the human-inflicted mortalities to Snake Basin salmon and steelhead. As required by multiple laws and treaties, the federal government has tried to mitigate the fatal impact of these eight dams. For the last 25 years, the federal government conducted a program of trapping young migrating fish at upstream dams and hauling the smolts in special barges down the Snake and Columbia for release below Bonneville dam.