Watercress Darter NWR was established by the Service in 1980 to provide protection for the watercress darter and to conserve and restore its crucial habitat. Today, the 24-acre refuge consists of two ponds, several stands of mixed pine-hardwoods with shrubs, and a single residence. Thomas Spring is a one-quarter-acre pond where a population of watercress darters was found in 1976. A second pond was constructed on the refuge in 1983 by the Service to provide additional habitat for the darter.

The watercress darter is a small, very colorful fish measuring up to 2.5 inches in length. The fish is found naturally in only four sites in the upper Black Warrior River drainage near Birmingham, Alabama. Watercress darters have been introduced and are reproducing in a fifth location. They are found only at mid-depths in dense accumulations of aquatic vegetation including watercress, in springs and spring runs. Green sunfish, bluegill, and sculpin are known to prey on watercress darters. The darters feed on snails, crustaceans, and insect larvae that inhabit springs and spring runs.

Watercress Darter NWR was established to protect Thomas Spring, one of only 4 known locations where the watercress darter was found naturally. Uplands around the spring contain a mixture of mature pine and hardwoods and dense understory of vegetation. The small size of the refuge (24 acres) and its location in a suburban setting, does not provide for a diversity of wildlife. The primary purpose of the refuge is the protection of Thomas Spring and its population of watercress darters.

The first population of watercress darters was collected at Glenn Springs in 1964. Additional field work has resulted in the location of three other populations: Thomas Spring (1976), Roebuck Springs (1978) and Seven Springs (2002). The greater Birmingham metropolitan areas encompass all of these sites, which are threatened with groundwater pollution and the presence of extensive impervious surfaces (e.g., roads, parking lots, and roofs), which divert water away from the recharge area of the springs? aquifers and lessens flows. In 1970, the Service officially recognized the watercress darter as an endangered species.

Little is known about the history of Thomas Spring, where Watercress Darter NWR is located, although it was apparently dammed up for about 20 years prior to the discovery of watercress darters. The damming of Thomas Spring created excellent habitat for the darters by providing slow-moving backwater that allowed dense aquatic vegetation to become established.

In 1977 the former landowner of Thomas Spring introduced grass carp (Ctenopharyngodon idellus), to clear the aquatic vegetation in the spring. By October, the grass carp had removed most of the spring's vegetation up to the shoreline. Only a single watercress darter was collected during sampling at this time. After refuge establishment in 1980, the grass carp were removed from Thomas Spring and the spring re-vegetated with Chara, Nitella, and Spirogyra in early 1981. Soon thereafter, the relocation of watercress darters from Glenn Springs to restock Thomas Spring was accomplished. On October 1, 1980, the U.S. Fish & Wildlife Service purchased 7 acres of property around Thomas Spring in Bessemer, Alabama to protect the watercress darter.

Today, Watercress Darter NWR contains 24 acres all surrounding Thomas Spring. In 1983 the refuge constructed a pond just downstream from Thomas Spring and vegetated the pond with appropriate aquatic plants for additional watercress darter habitat. In January 1988, 100 watercress darters were relocated from Thomas Spring into this newly constructed pond. Prior to federal acquisition Thomas Spring was privately owned and located in rural Jefferson County Alabama.

The City of Bessemer has since grown to include the area containing Thomas Spring. Impacts associated with urban development are the primary force impacting watercress darter in all of their known locations.