Why do salmon swim upstream?

Answer: Spawning in birthplace

Searching for more food — Wrong. Salmon don't feed during the spawning migration—they rely on stored energy. The upstream journey is driven by reproduction, not foraging.

Spawning in birthplace ✓ — Correct! Salmon return to the stream where they hatched to spawn. As young fish they imprint on its particular smell, and years later they follow that scent upstream, sometimes hundreds of miles against the current and over waterfalls, to gravel beds where their eggs can develop. They are anadromous: born in fresh water, grown in the sea, back to fresh water to breed. Pacific salmon spawn once and die, having spent nearly everything on the journey, whereas Atlantic salmon and steelhead can survive, return to the sea and spawn again. In the ocean, a magnetic sense helps them find their way back toward the coast.

Escaping ocean predators — Wrong. The ocean does have predators, but swimming upstream is about reproduction—returning to natal streams to spawn, not fleeing danger.