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The objectives and scope of the NASQAN program have changed several times since its beginnings in 1973 to reflect changes in funding, technology, and societal priorities and needs. The latest design for NASQAN was implemented in October 2007. Under this design, the major objective of the NASQAN program is to report on the concentrations and loads of selected constituents delivered by major rivers to the coastal waters of the United States and selected inland sub-basins in priority river basins to determine the sources and relative yields of constituents within these basins. These priority basins have significant management interest in reducing delivery of constituents that contribute to adverse conditions in receiving waters. Other objectives include monitoring for climate change and describing long-term trends in the loads and concentrations of select constituents at key locations.