The snail darter controversy related to the discovery in 1973 of an endangered species during the construction of the Tellico Dam on the Little Tennessee River; the dam project had been authorized and begun before passage of protective environmental legislation. On August 12, 1973, University of Tennessee biologist and professor David Etnier discovered the snail darter in the Little Tennessee River while doing research related to a lawsuit under the National Environmental Policy Act (NEPA). The lawsuit said that the Tellico Reservoir, to be created by Tellico Dam, would alter the habitat of the river to the point of killing off the endangered snail darter.

The Little Tennessee River is a 135-mile (217 km) tributary of the Tennessee River that flows through the Blue Ridge Mountains from Georgia, into North Carolina, and then into Tennessee, in the southeastern United States. It drains portions of three national forests— Chattahoochee, Nantahala, and Cherokee— and provides the southwestern boundary of the Great Smoky Mountains National Park.