The seasonal development of a zone of hypoxia in the Gulf of Mexico, which poses a threat to commercial aquatic communities, has been associated with nutrient loadings from the Mississippi River. This oxygen-depleted zone occurs in bottom-waters and currently includes an area of approximately 7000 square miles, extending from the mouth of the Mississippi River, westward along the coast towards the Texas border. The Ohio River Basin constitutes approximately 20 percent of the Mississippi Watershed, and contributes about 35 percent of the river's total flow. It is therefore logical to suspect that nutrient loadings from the Ohio River could be contributing to eutrophication problems in the Gulf. In the fall of 1997, the Ohio River Basin Water Sanitation Commission (ORSANCO) began conducting a study to evaluate nutrient loads and sources in the Ohio River Basin. The objectives of this project are to document present water quality conditions concerning nutrients in the Ohio River and its major tributaries, to quantify nutrient loads from major sub-basins to the Ohio River through water quality monitoring activities, and to assess the relative magnitude of nutrient sources (i.e., agriculture, POTWs, industrial discharges, urban runoff, etc.). In addition, the identification of priority watersheds within the Ohio River Basin will provide a basis for implementing and measuring the effectiveness of control programs to reduce stream nutrient loads in the Ohio River Basin and, ultimately, to the Gulf of Mexico.