We know now that overfishing, combined with habitat destruction, was one of the first causes of salmon decline. Harvest today is highly regulated but can still be a problem when endangered stocks are caught unintentionally with non-endangered ones. Technology has made it possible to harvest many or even all the fish. Fishing must be carefully managed so that salmon continue to be a harvestable resource. Hydropower - Hydroelectric dams block migration to and from the ocean.
Many dams lack fish ladders.
The downstream migration of young salmon is hampered by the huge reservoirs of water that form behind dams where juvenile fish are exposed to unhealthy conditions, high temperatures and predators. Fish that pass through the turbine blades of dams are often injured or killed. Hatcheries - Hatcheries developed as a way to compensate for the loss of salmon habitat to dams, agriculture and urbanization. They effectively protect salmon eggs and rear young fish to the time of freshwater release. At that point, salmon must cope with whatever conditions exist for the downstream migration, in the ocean and, later, as they return to spawning grounds.