Each year the sockeye salmon return to their birth spot to continue life's cycle and lay their eggs. Once they leave the Pacific Ocean they don't eat and live only on their body fat, so by the time they reach here they are tired and weak. Just strong enough to lay eggs, or fertilize them.
In the bottom picture, the water is cloudy as the male is spreading his milt (or fertilizing) the recently laid eggs of the female.

(This river is in the central interior of British Columbia, Canada)

Credit: {Hues} Perfectly Pumpkin by Connie Prince