From the USGS:
A new U.S. Geological Survey interactive map provides a comprehensive, long-term look at changes in the quality of our nation’s rivers and streams over the last four decades.
For the first time, monitoring data collected by the USGS and 73 other organizations at almost 1,400 sites have been combined to provide a nationwide look at changes in the quality of our rivers and streams between the 1972 passage of the Clean Water Act and 2012.
The interactive map can be used to see whether 51 water-quality constituents, like nutrients and pesticides, and 38 aquatic-life metrics, like the types and numbers of fish, macroinvertebrates, and algae, have increased, decreased, or remained the same at nearly 1,400 sites between 1972 and 2012. For example, the phaseout of the insecticide diazinon for residential and some agricultural uses was initiated in 2000 and has led to widespread reductions in concentrations in U.S. streams, which can be seen on the map during the trend period from 2002 to 2012.
This map was developed by the USGS National Water-Quality Assessment Project, which conducts regional and national assessments of the nation’s water quality to provide an understanding of current water-quality conditions, whether conditions are getting better or worse over time, and how natural processes and human activities affect those conditions.
Direct to New USGS Map
See Also: More Interactive Maps From USGS