In earlier work under the sponsorship of EPA, loading functions were developed by Midwest Research Institute (MRI) for estimating the quantities of different diffuse loads entering receiving waters from nonpoint sources and a screening methodology was produced by Tetra Tech, Inc., for assessing water quality problems in areas not covered under Section 208 of the Federal Water Pollution Control Act Amendments of 1972. The two methods had never been applied together under realistic conditions, however, to demonstrate how the combined techniques might be used for identification of water quality problems in U.S. rivers. In this report, the successful application of the MRI-developed nonpoint loading procedures under field conditions in five river basins is described and the compatibility of these procedures with the 208 screening methodology is demonstrated. The basins in which the assessment techniques were used were the Sandusky River in Ohio and four Chesapeake Bay Basins (Patuxent, Chester, Occoquan, and Ware Rivers).