Too hot

Lower Snake River water temperature during the summer is too hot for salmon migration. For the last 20 years, over 64 percent of the time during the summer, water temperature is too hot and exceeds 68 degrees. Higher water temperatures during migration increases prespawning mortality and deplete energy reserves before fish reach spawning grounds, reducing the size and number of viable eggs. The Snake River does not have enough adult salmon returning to prevent extinction and hot water kills adult salmon migrating up the Snake River. The Snake River has the hottest temperature during the upstream migration of adult chinook and sockeye salmon.