August 24, 2026 — For California’s most endangered salmon, the difference between surviving and dying may come down to just 15 days.
In a study published Friday in Science Advances, researchers say the chance of juveniles surviving fell by about 73% for every 1.8-degree Fahrenheit increase in average river temperature during those first 15 days.
Sacramento River winter-run Chinook have only one surviving population, with an average of a few thousand fish returning in recent decades.
Shasta Dam keeps the salmon from returning to their original cold-water habitat around Mount Shasta in Northern California. Instead, they spawn in the Sacramento River, where warmer summer water can threaten their developing eggs.
Cold water is released from Shasta Reservoir to keep the river cool enough for salmon eggs to survive, but that water is also needed by farms and cities.
The balance becomes harder in dry years, when there’s less water to go around.
Kohma Arai, who conducted the research as a postdoctoral scholar at UC Davis, said a full summer of spawning doesn’t necessarily mean a successful season.