How do natural features and human activities affect the quality of streams and ground water?
Major river basins and aquifers across the Nation define NAWQA “study units” (see maps). Within these areas, USGS scientists collect and analyze information on water chemistry, hydrology, land use, stream habitat, and aquatic life. Each study-unit assessment is an interdisciplinary and long-term evaluation of the total resource, rather than a short-term study of a specific geographic area or problem at a single point in time. NAWQA findings thereby describe the general health of water resources, as well as current and emerging water issues—information that is essential for developing practical management strategies for protecting and restoring water quality. Because each study-unit assessment adheres to a national design and nationally consistent sampling and analytical methods, water-quality conditions in a specific locality or watershed can be compared to those in other geographic regions and at different periods of time. Collectively, the assessments advance an understanding of the
