For example, salmon and steelhead spawn and live for a time in a stream before going to the ocean. They require an ample supply of clean, cool, well oxygenated water. Vegetated streambanks shade the water from the warming effects of the sun.
Insects drop off overhanging vegetation and provide food.
When juvenile salmon or steelhead enter saltwater, their habitat requirements change. During this critical transition period, they must have shallow, near-shore waters where they can migrate, school, feed, and seek protection from larger fish. Each species of fish and shellfish has similar, yet unique requirements. They have become adapted to and require these natural conditions as a result of the 10,000 years of evolution since the last ice age. The degradation of any one of the elements of their required habitat results in reduced numbers of fish and shellfish.