There are many ways humans can cause damage to fish habitat. Sometimes it is done on a large scale. At other times the activities of individuals can seriously impact fish habitat. Improper siting or construction of bridges, dikes, and culverts can funnel water flow in a stream or river. If not properly installed, these structures can increase water speed so much that fish cannot get upstream.
Culverts perched above the level of the stream bed can also prevent fish migration upstream.
Construction projects that remove or reroute large amounts of water or gravel can severely damage fish habitat. Rerouting the stream can create pools in which fish get stranded and die. If properly done, most of these activities can have little impact, enhance, or create needed habitat for fish. Another activity that can affect fish survival is the removal of natural vegetation from stream banks. The result is loss of cover and food for fish.