Snake River Dams

Water flows through a channel designed to help migrating fish swim through the Lower Granite Dam on the Snake River near Almota, Wash., in this 2018 photo.

LEWISTON, Idaho (AP) — An Environmental Protection Agency report details how federal dams in the Snake and Columbia river system raise summertime water temperatures and hurt endangered salmon runs.

The report, made public Tuesday, said dams on both rivers play a role in raising water temperatures above 68 degrees, at which point the heat becomes harmful to salmon and steelhead.

The Lewiston Tribune said the report also noted that the Snake River often exceeds temperature standards before it enters Washington from Idaho, as does the Columbia River when it enters Washington from Canada.

The report is likely to influence a long-brewing debate over the role dams play in the decline of threatened and endangered salmon and steelhead.

The dams generate electricity, allow cargo to be moved on river barges and provide irrigation water to farmers. By slowing the water’s flow and increasing the surface area exposed to the sun, the dams cause the Snake River temperature to increase by as much as 5.7 degrees, the report states.

Temperatures higher than 68 degrees can cause adult fish to stop and swim aimlessly, as if lost, during their return migrations from the ocean. Rivers that warmed into the 70s in 2015 and stayed there for weeks saw significant fish kills.

While there are other causes of temperature increases in the river, dams play the largest role, the report said.

Environmental groups hailed the report as a needed step toward improving conditions for salmon and steelhead.

Following the 2015 heat event that killed off sockeye, a coalition of river preservation groups — including Columbia Riverkeeper, Snake River Waterkeeper and Idaho Rivers United — went to court to force the EPA to finish the report that had been stalled for nearly two decades.

“We are pleased that it’s done and identifies the hot water problems on the Columbia and Snake rivers,” said Brett VandenHeuvel of Columbia Riverkeeper.

Environmental groups have long called for four dams on the Snake River in eastern Washington to be removed to help salmon and steelhead migrate to the ocean and back. But the dams have plenty of supporters, including some members of Congress and business groups.

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