Most salmon start to swim upriver during late spring and summer but won’t spawn before fall or early winter. The exact time of spawning depends on factors such as water temperature, oxygen level, type of habitat, and type of salmon.
All Pacific salmon and a majority of Atlantic salmon die after they have spawned. They basically stop eating and use up all of their energy when swimming upstream against the strong current. Once they are done spawning, their bodies keep deteriorating until death.