Technical Abstract: Remediating non-point source pollution in agricultural watersheds remains an intransigent problem worldwide. Conservation and research in an agricultural watershed above the Fort Cobb Reservoir in southwestern Oklahoma serves as a case study in how a multitude of players address such a challenge. The reservoir, managed by the Bureau of Reclamation for drinking-water supply, flood control, recreation, and fish and wildlife habitat, fails to meet state water quality standards based on hypertrophic condition in summer months. In 2001, the Oklahoma Conservation Commission and Natural Resources Conservation Service (NRCS), conservation districts, and landowners focused conservation efforts to decrease sediment and phosphorus delivery to the reservoir. By 2005, estimated phosphorus loading decreased by 20% and water quality in tributary creeks had improved. The improvements were described as a Nonpoint Source Program Success Story by the U.S. Environmental Protection Agency. In 2003, NRCS and the Agricultural Research Service (ARS) selected Fort Cobb watershed as a Benchmark Watershed under the Conservation Effectiveness Assessment Project (CEAP), a national effort to quantify environmental benefits of agricultural conservation. Selection was based on a multitude of prior monitoring and research in the watershed. Under CEAP, additional U.S. Geological Survey (USGS) streamflow-gaging stations, water quality sampling under low and high flow conditions, and weather monitoring stations were established, and information about conservation practices implemented in the watershed was compiled. In 2004, the USGS Biology, Geography, Geology, and Water Science Centers, in collaboration with ARS, began inter-disciplinary research to complement ongoing efforts and produce an integrated product that could support planning, implementing, and monitoring the success of BMPs. This publication provides a collection of reports discussing climate, soils, geology, data describing water quality in streams and the reservoir, land use and cover, and surface materials affecting water quality. Also included are a database of historical imagery available for the watershed and a compilation of environmental data collected by state and federal agencies.