Animals that live in a stream are adapted to life in the fast lane. Brook trout have strong, streamlined bodies and powerful tail fins that can push against the current. These fish need the cold, oxygen-rich water of a flowing stream in order to thrive. Shade is very important in keeping the stream cold. When forest fires, lumbering, or road building make streams lose their shade, they also lose their trout.
Atlantic salmon are famous for their ability to buck the current.
They swim upstream in spring in order to lay their eggs on the gravel bottom where they were born. Where man-made dams block their route, they will dash themselves to death against the concrete walls trying to leap over them. On some rivers in Maine, fish ladders help anadromous fish continue their journey. These are fish, such as salmon, shad, and herring, which spend part of their lives in the ocean, but return to fresh water to reproduce. Fish hatcheries rear small salmon called smolts to help stock Maine streams where salmon once were plentiful.