National Water-Quality Assessment Program (NAWQA)
In 1991 the U.S. Geological Survey initiated the National Water-Quality Assessment (NAWQA) Program to assess the status and trends in the quality of freshwater streams and aquifers, and to provide a sound understanding of the natural and human factors that affect the quality of these resources. As part of the program, investigations will be conducted in 59 areas-- called "study units"-- throughout the Nation to provide a framework for national and regional water-quality assessment. Together, these areas account for 60 to 70 percent of the Nation's water use and population served by public water supplies, and cover about one-half of the land area of the Nation.
NAWQA Studies in California