Adding a large amount of spawning habitat would be a major benefit to breaching the four lower Snake River dams, primarily for fall Chinook salmon. Historically, fall Chinook spawned extensively in the mainstem Snake River above Hells Canyon. That spawning habitat was lost when the three-dam Hells Canyon Complex was built by Idaho Power in the 1960s creating an impassable fish barrier. Additional fall Chinook salmon spawning habitat was lost when Dworshak dam was built blocking access to the North Fork Clearwater River.  

Consequently, the spawning habitat currently available to fall Chinook salmon is quite limited.  This is reflected in the Columbia Basin Partnership’s high-end goal of only 23,360 wild fall Chinook. This contrasts sharply with the Nez Perce Tribe’s estimate of approximately 500,000 fall Chinook salmon produced in the Snake River system prior to the arrival of settlers of European descent.

Restoring 140 miles of the lower Snake River to its free-flowing state would create new fall Chinook salmon spawning habitat, increasing the potential for wild fall Chinook production. In particular, the habitat currently inundated by Lower Granite and Little Goose dams, the two dams furthest upriver, likely fostered important diversity in spawn timing. Restored spawning habitat is a major additional benefit of dam breaching beyond improvement in migration survival.