Davis Branch in Cumberland Gap National Historical Park was considered important for the recovery of the Federally threatened Chrosomus cumberlandensis (Blackside Dace). Monitoring of the Davis Branch population began in 1990. Castor canadensis (North American Beaver) colonization was reported in 1994, and a series of dams have persisted in the upper section of the stream. The pervasive effects of Beavers on Blackside Dace populations were unknown. Our goals were: 1) to characterize the fish community structure and relative abundance of Blackside Dace within the assemblage, 2) to determine the direct and indirect effects of beaver dams on the fish community, and Blackside Dace population, 3) to monitor the age structure of the Blackside Dace population, and 4) to recommend management actions that will enhance the Blackside Dace population within Davis Branch. Fishes were collected from eight stations annually from 1990–2010, except for 2003–2005. Stations were delineated within downstream and upstream sections based on Beaver presence, and within three periods, prior (1990–1993), post (1994–2002), and recent (2006–2010). Fish community structure indicated distinct downstream and upstream assemblages prior to Beaver colonization, with the relative abundance of Blackside Dace approximately 6% and 18%, respectively. The fish assemblage and relative abundance of Blackside Dace shifted over time, with the relative abundance of Lepomis gulosus (Warmouth), Lepomis auritus (Redbreast Sunfish), and Chrosomus erythrogaster (Southern Redbelly Dace) increasing, and Blackside Dace decreasing; only 25 Blackside Dace were encountered from 2006–2010. Comparison of Blackside Dace age classes between the 3 periods indicated the 0 age class decreased over time and 1 and 2 age classes increased initially but eventually declined within both the downstream and upstream sections. It is speculated that the continued presence of beaver dams increased stream temperatures downstream and upstream, altered the flow regime, and changed the available habitat, thus creating conditions more suitable for centrarchid species and Southern Redbelly Dace, which probably preyed upon and out-competed Blackside Dace, respectively. It is recommended that the National Park Service and its partners 1) develop a Beaver management program, 2) return Davis Branch to its free-flowing, pre-Beaver condition, 3) significantly decrease nonnative species and decrease native centrarchid species to abundances prior to Beaver colonization, and 4) establish a Davis Branch Blackside Dace propagation and reintroduction program.