The Lower St. Louis River Basin from Brookston to Lake Superior was sampled in late 1973. The resultant data were combined with historical data for verification of a water quality model--the St. Louis River Basin Model. The model was used to evaluate the effect on water quality of implementing effluent limits using best practicable technology and best available technology for industrial discharges, and secondary treatment for municipal waste sources, as required by the 1972 Amendments to the Federal Water Pollution Act. The study indicates that implementation of the above effluent limits, as well as utilization of a centralized treatment plant of advanced design, will result in a significant improvement in water quality in the Lower St. Louis River. However, with current benthic oxygen demand rates, DO in the reservoirs is projected to border on noncompliance at summer low flow, even with essentially zero discharge of pollutants from industrial and municipal sources in the Cloquet area.