An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

National Aquatic Resource Surveys

What is the National Wetland Condition Assessment?

Wetlands are a vital component of our nation’s waters, providing a wide array of benefits that contribute to the overall health and integrity of aquatic ecosystems and people’s well-being. Though we are aware of the important benefits wetlands provide, we know very little about their actual ecological health. The National Wetland Condition Assessment (NWCA) is a statistical survey that begins to address some of the gaps in our understanding of wetland health by providing information on the ecological condition of the nation’s wetlands and stressors most commonly associated with poor condition.

The NWCA is designed to answer basic questions about the extent to which our nation’s wetlands support healthy ecological conditions and the prevalence of key stressors at the national and regional scale. It is intended to complement and build upon the achievements of the U.S. Fish and Wildlife Service Wetland Status and Trends Program, which characterizes changes in wetland acreage across the conterminous United States. Paired together, these two efforts provide government agencies, wetland scientists, and the public with comparable, scientifically-defensible information documenting the current status and, ultimately, trends in both wetland quantity (i.e., area) and quality (i.e., ecological condition).

The 2011 National Wetland Condition Assessment was the first national evaluation of the ecological condition of the nation’s wetlands. NWCA field season sampling is conducted every five years.

Survey Design

The sampling design for the NWCA is a probability-based network that provides statistically-valid estimates of ecological condition for a population of wetlands with known confidence. Sample points are selected at random to represent the condition of wetlands across the country. The survey design is developed in partnership with the US FWS Wetlands Status and Trends Program.

The NWCA sampling is comprised of all wetlands of the conterminous U.S. The survey encompasses both tidal and nontidal wetlands ranging from the expansive marshes of our coasts to the forested swamps, meadows, and waterfowl-rich prairie potholes of the interior plains.

View more details about the survey design in the design documents.

The use of standardized field and laboratory protocols is a key feature of the NWCA and allows the data to be combined to produce a nationally consistent assessment. As part of the quality assurance procedures, each field crew was trained and evaluated on applying the NWCA protocols by wetland experts.


The 2011 NWCA collected data to characterize biological, chemical, and physical features of each site. Vegetation, soil, hydrology, water chemistry, algae, and buffer characteristics were chosen for evaluation based on their utility in reflecting ecological condition of wetlands or key indicators of stress that may influence condition across broad national and regional scales. Data for each of these indicator groups were obtained from field observations, field samples collected at wetland sites, and laboratory analyses of field samples.

For general descriptions of the indicators used for NWCA as well as those used in the coastal survey (NCCA), the lakes survey (NLA), and the rivers and streams survey (NRSA), please visit the Indicators used in the National Aquatic Resource Surveys page.