Agricultural nonpoint sources of nutrients and sediment threaten the quality of the Cane Creek Reservoir, a Piedmont North Carolina water supply lake, in the absence of detailed monitoring, the Agricultural NonPoint Source Pollution Model (AGNPS) was used to predict water runoff and the delivery of dissolved and sediment-attached nitrogen and phosphorus to stream tributaries to the lake. The findings of the distributed parameter modeling study included four dairy watersheds (53 to 195 ha) and were part of a management plan developed to protect the impoundment from further degradation. Annual total nitrogen and total phosphorus export predictions for entire farms ranged from 1.0 to 3.7 and 0.7 to 1.8 kg · ha−1for current conditions. Simulated exports of total nitrogen and total phosphorus were between 0.9 to 3.1 and between 0.4 to 1.6 kg · ha−1due to best management practices (BMPs) installed. In addition, simulation studies of smaller areas such as individual pastures, cropland fields, and feedlots showed substantial nutrient export reductions due to refinements in dairy manure management, depending upon the site. For one feedlot needing structural improvements, simulated BMPs reduced annual total nitrogen and total phosphorus loads from 74 and 21 kg · ha−1to 0.85 and 0.4 kg · ha−1. Also included are recommendations for additional BMPs and the cost for implementation.