The fish popularly known as darters are small, perch-like fish found in freshwater streams in North America. They are members of the family Percidae and include members of the Ammocrypta, Crystallaria, Etheostoma and Percina genera. Some darters are widespread throughout North America, most notably in the Mississippi Basin, but others are restricted to single streams, leaving them vulnerable to extinction. Each river basin has for the most part it own sets of darters. The darters are cold watered fish that do not take to pollution very well. This causes problems when there are cities and contaminants in river basins. For this reason many darters and extinct or endangered.