This means the City of Portland must act to protect salmon , because the Columbia River system includes rivers and streams in the Portland area. One important reason for the declining number of Chinook is the steady loss of their natural habitat. Development, erosion, and activities that pollute water all have all helped destroy Chinook habitat. Chinook are anadromous fish, which means they are born in freshwater, migrate to the ocean, then return to freshwater to spawn.
Anadromous fish benefit from both freshwater and marine habitats.
Freshwater streams have fewer predators and are safer for the development of young fish. Marine habitats have more abundant food and may support more rapid growth and larger fish. Habitat Requirements Chinook, like all salmon, need clean, cool water with plenty of oxygen and low amounts of suspended solids and contaminants. They also need gravel and rocks to spawn. Fine sediment can be lethal to Chinook.