A salmon can detect one drop of water from its home stream mixed up in 250 gallons of sea water. Salmon will follow this faint scent trail back to their home stream to spawn. The lateral line along the salmon's side can detect very small currents in the water. This helps them tell direction, find food, and avoid predators. Some Sockeye salmon are able to navigate using the sun and moon. Salmon have 300 degree vision. They can see in all directions except directly behind them.
Text by USFWS