USGS NAWQA: About Regional Assessments on Water-Quality Status and Trends

Status and trends of surface-water-quality are assessed within eight large geographical regions, referred to as “major river basins” covering the U.S. Status and trends of ground-water-quality are assessed within about one-third of the Nation’s 62 principal aquifer systems. Results are reported by major river basin and principal aquifer system, as well as compared across the regional systems for a national perspective. The reports highlight regional differences in land use, geology, and climate that lead to regional differences in water quality.

NAWQA’s approach to assessing status and trends implements several modifications from its approach used from 1991 through 2006, including: (1) a shift in the scale of data analysis and reporting from 42 Study Units to 8 larger “major river basins” and principal aquifers; (2) incorporation of modeling with monitoring to help extend water-quality understanding of conditions, sources, and transport to unmonitored, yet comparable areas; and, (3) collaboration and integration of data from other Federal agencies, as well as regional, State, Tribal, and local organizations. Such modifications help to meet funding reductions and to maximize the use of its stream-monitoring information for broad water-resource understanding.