Water flow depends on the slope of the land. Younger rivers tend to have steep slopes, fast-moving water and narrow floodplains. Older, larger rivers carry more sediment, flood larger areas of nearby land, and have only periodic rapids or riffles. Water striders, whirligig beetles and others use the water tension to ride the surface of rivers. Beaver and muskrat burrow into streambanks, while clams and worms hide among rocks and in sandy bottoms.
Animals react to the flowing water in a variety of ways.
Some have shapes and methods of locomotion that allow them to swim against the current, like the rainbow trout in the River Olympians exhibit. Some fish that cannot swim against the current avoid it by staying close to the bottom and behind rocks, like darters and sculpins. Others, among them bluegills and other sunfish, congregate in the slow-moving waters under trees and at the inside of bends in the river. Students will infer the relationship between streamlining in air and in water. Finally, students will interpret reasons for different fish shapes in varied aquatic environments, and understand that animals and their natural habitats are well matched to each other.