Watercourse aquifer systems in many areas are adversely affected by wastes disposed into surface‐water sources, resulting in either reduced streambed permeability, infiltration of wastes into the aquifer, or both. These conditions are illustrated at Lancaster, Ohio, where low streambed permeability in the vicinity of the municipal well field, resulting from the discharge of wastes to the Hocking River, seriously retards the infiltration of surface water and lessens the available yield of the wells. The wastes consist of brine and iron‐laden effluent from the municipal treatment plant, discharged within the area of influence of the pumped wells to a stream already carrying much organic waste and other debris. Upstream from the discharge sewer, muck and organic debris have accumulated thickly on the streambed, while downstream from the sewer the streambed sediments have become tightly cemented by iron and other constituents in the waste water. There is evidence that, despite reduced streambed permeability, wastes have entered the aquifer and have materially contributed to declines in well efficiency and to recurring problems of well maintenance. Conditions such as those illustrated at Lancaster occur also at Dayton and are not uncommon elsewhere in Ohio. Indirect contamination of aquifers and adverse physical and chemical alteration of streambed sediments, resulting from surface‐water waste disposal, may in many places pose a threat to the ground‐water supply. This fact should not be overlooked in determining water‐quality standards to be established under the Water Quality Act of 1965.