Snail darters are a large river species, mostly found in the upper TN river (and larger tribs):
http://nas.er.usgs.gov/queries/facts...?SpeciesID=827
Fishes of TN (Etnier and Starnes) is a great book. See if you can get a copy loaned to your library, if it is not already on the shelf.
There is over 300 species of fish in TN. Many of them are darters and are common and live in creeks.
More than likely you probably saw central stonerollers, a very common creek inhabitant.