The snail darter (Percina tanasi) is a species of fish that is found in East Tennessee freshwater in the United States. It is in the perch family (family Percidae) of the order Perciformes. Discovered in 1973, the snail darter was listed as endangered under the U.S. Endangered Species Act of 1973 by 1975 and was involved in a legal controversy leading to a Supreme Court ruling to halt the completion of Tellico Dam, which posed a risk of extinction for the snail darter by blocking its migratory route — see Tennessee Valley Authority v. Hill, snail darter controversy.