Chinook salmon
The Powder River was once an important spawning stream for Chinook salmon ("Oncorhynchus tshawytscha") and steelhead trout ("Oncorhyncus mykiss") coming from the Pacific Ocean. Chinook salmon once migrated by the thousands to spawn in the Powder River and many of its tributaries from its headwaters to the lower end of the North Powder Valley, but that stopped when the Thief Valley Dam was built near North Powder in 1931. The building of two later dams in Hells Canyon on the Snake River – Hells Canyon Dam (1967) and Brownlee Dam also permanently block salmon passage. The Oregon Department of Fish and Wildlife often release Chinook salmon on the Powder River for sportfishing at Mason Dam below Phillips Reservoir.