The Maryland darter (Etheostoma sellare) is considered one of the rarest freshwater fish species in the world, due in part to its incredibly limited geographic range and difficulty of detection. The last sighting of one was in 1988. The Maryland darter is named after the only state in which it is known to occur. The species was long known only by two specimens until being "re-discovered" in 1962. From 1965 into the 1980s, the species was believed to have been confined to a single riffle in Deer Creek. Possible explanations for the decline of the species center around widespread habitat degradation and reduction in water quality resulting from increasing rates of urbanization within the watershed. While the IUCN has declared the species extinct, the United States Fish and Wildlife Service h