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River Health

National Rivers and Streams Assessment – Probabilistic Study

The NRSA is a statistical assessment of the condition of the Nation's 3.5 million miles of flowing waters sponsored by the U.S. Environmental Protection Agency (EPA) and is designed to:

  • Assess the condition of the Nations perennial streams and rivers;
  • Assess the extent and impact of major environmental stressors of flowing water;
  • Evaluate changes in conditions of the Nation's rivers and streams over time:
  • Help build State and Tribal capacities for monitoring and assessment, and promote collaboration across jurisdictional boundaries.

Monitoring Objectives

The primary objectives of the NRSA surveys are to generate statistically-valid reports on the conditions of the Nation's streams and rivers, identify key factors (stressors) impacting the physical, chemical, and biological conditions of flowing waters in the U.S., and assess changes in the condition of these resources over time.

Monitoring Design

The NRSA is conducted on a 5 – year cycle, using nationally – consistent field protocols and data interpretation. The most recent survey period was 2013 – 2014. A total of 1,800 sites randomly-distributed across the 48 contiguous states were selected to characterize the Nations streams and rivers. The sites are stratified by 9 national ecoregions and by waterbody size (wadeable and boatable). For NRSA 2013-2014, Wisconsin was assigned 25 wadeable and 31 boatable sites to be samples as part of the national survey population. To develop a statistically-robust sample size for Wisconsin, an additional 25 randomly – selected wadeable stream sites, (for a total of 50 wadeable sites), and an additional 10 boatable sites were also surveyed (total of 41 boatable sites).

Water Quality Indicators

Physical, chemical, and biological parameters measured:

  • Core Indicators
    • Physical habitat (in-stream and riparian)
    • Water temperature, pH, conductivity, and dissolved oxygen
    • Water chemistry grab samples (nutrients, sediment, etc.)
    • Benthic macroinvertebrates
    • Fish assemblage data
  • Supplemental Indicators
    • Algal toxins (Microcystin)
    • Fecal Indicators (Enterococci)
    • Fish Tissue Plugs (methylmercury)
    • Whole Fish (legacy pollutants such as poly-chlorinated biphenyls)

Field Samples and Data Management

NRSA physical habitat data are recorded on field forms developed by EPA. Completed forms are sent to EPA and scanned to capture these field data. EPA subsequently distributes these data and interpretations electronically to the states. Water chemistry samples including algal toxins and enterococci were processed by the Wisconsin State Laboratory of Hygiene and results are captured in SWIMS and reported to EPA. Macroinvertebrate samples are processed by a Wisconsin university lab and data are also captured in SWIMS and reported to EPA. Fish assemblage data are entered in to the department's Fisheries Program database that is linked to SWIMS. Fish tissue plugs and whole fish are processed by an EPA contract lab and will be captured in SWIMS.

Data Management

Data are collected and sent to USEPA. Eventually, DNR would like all data stored in SWIMS.


EPA releases a nationwide report following each NRSA survey. WDNR researchers present Wisconsin-specific results in the form of oral presentations and posters at statewide meetings and national conferences. NRSA results are also included in the Integrated Report. In the future, NRSA results will also be reported on the WDNR website.

Programmatic Evaluation

Apart from EPA evaluations, WDNR will assess probabilistic monitoring every five years.

Last revised:

Tuesday May 30 2017