The National Water Quality Network (NWQN) for Rivers and Streams includes 105 sites monitored by the U.S. Geological Survey (USGS) National Water Quality Program (https://www.usgs.gov/mission-areas/water-resources/science/usgs-nationa…). This data release provides streamflow, nutrient, and sediment data collected and analyzed by USGS for one Mississippi River site and one Atchafalaya River site used to represent contributions to the Gulf of America because of their long-term datasets and locations downstream of the Old River Outflow Channel. This dataset includes daily, monthly, and annual summaries of streamflow conditions, discrete water-quality concentrations, annual water-quality loads, and information on water-quality trends. Trends in flow-normalized water-quality constituent loading to the Gulf of America were estimated for a period starting in a baseline period (mean of 1980 to 1996) and ending in 2025. There is data included in this data release from before 1980 that was used as model input data. Water-quality data were collected at USGS sites 07373420 Mississippi River near St. Francisville, LA and 07381495 (COE) Atchafalaya River at Melville, LA. Streamflow data were collected at U.S. Army Corps of Engineers sites 01100Q Mississippi River at Tarbert Landing and 03045Q Atchafalaya River at Simmesport.
