National Aquatic Resource Surveys (NARS): the foundation for long-term aquatic monitoring data across the United States.

There is a common saying in business that "what matters gets measured". Environmental protection and sustainability certainly should qualify as important concerns for both businesses and governments. The 1970s marked the genesis of the modern environmental movement, with growing concern about water pollution in the United States (U.S.). In 1972, the U.S. enacted the Clean Water Act (CWA) "to restore and maintain the chemical, physical, and biological integrity of the Nation's waters". In accordance with CWA objectives, the U.S. Environmental Protection Agency (EPA) implemented the surface water and estuary regional research components as part of the Environmental Monitoring and Assessment Program (EMAP), from which the National Aquatic Resource Surveys (NARS) evolved. NARS is designed to assess the condition of all the Nation's aquatic ecosystems, including lakes and reservoirs, rivers and streams, coastal waters, the Great Lakes, and wetlands. NARS is the only long-term program that, in collaboration with states and Tribes, monitors the chemical, physical, and biological integrity of the Nation's aquatic ecosystems using a statistical survey design and consistent field protocols. In this article, we discuss why NARS exists, its key objectives, how NARS has influenced monitoring of natural resources, and how NARS data are used to support U.S. research and policy decisions at broad spatial and temporal extents. We also provide specific examples of how NARS data support condition and risk reporting of indicators, including benthic macroinvertebrates and water surface total phosphorus, and development of tools for characterizing emerging concerns, such as harmful algal blooms (HABs) and antibiotic resistance genes (ARGs).