Partly due to the Marine Mammals Protection Act, Sea Lion populations in the Northwest have soared. Although commercial fishing is now restricted much more than it has been in the past, sophisticated fishing techniques produce a large harvest every year. Some salmon are caught illegally by open sea drift nets. Then salmon face the challenge of getting back upstream to their spawning ground, almost always the exact same place where they were born. Often Sea Lions or nets are waiting for them at the mouths of rivers.
Dams often slow and sometimes block salmon from moving upstream.
Because of development around streams and rivers, water which would ordinarily be absorbed into the ground goes into rivers, flooding them. This flooding sometimes washes away spawning beds and can cause salmon to wander off a main river channel and lay eggs in areas that will later dry up. In the wild, from each nest of eggs, two adult salmon could be expected to return several years later to spawn. However, with human interference, it is difficult for the salmon to maintain this state of equilibrium.