Summary: Accurate, reliable data on the actual condition of the nation's rivers and streams are necessary for sound environmental planning and management. Existing national water quality monitoring networks do not provide the type or quality of data needed.
Water quality can change dramatically during 1 day, and within a short distance. Complex interactions among biological, chemical, and physical processes complicate the difficulties of water quality sampling. Infrequent measurements cannot accurately describe water quality, because rivers can change rapidly and extensively. Infrequent sampling also misses important events. Cost has been a major consideration in decisions on sampling frequencies. Each sampling site is affected by unique conditions, and water quality measurements taken at one site cannot normally be applied to other locations, not even those nearby in the same river. The Geological Survey focuses primarily on riverflow, not water quality. Stations are located toward the downstream end of drainage basins. The Survey does not intend to detect any particular category of water quality, water use, or related land use. The Survey, the Environmental Protection Agency (EPA) and the Council of Environmental Quality (CEQ) have used network data in statistical comparisons of water quality, but these comparisons are highly questionable. The variability of water quality, the limited frequency and locations of samples, and the inconsistency in field work and laboratory performance make it virtually impossible to compare the data meaningfully from month to month, season to season, and year to year. Special studies of water quality designed for individual river areas could overcome many weaknesses inherent in the sampling techniques.
