Understanding the quality of U.S. streams, rivers, and groundwater requires consistent data collection and analysis over decades for proper context of current conditions. The USGS collects nationally standardized data and information as part of the National Water Quality Network (NWQN). The NQWN is made up of sites across the Nation where USGS scientists regularly measure water-quality conditions.
The National Water Quality Network (NWQN) is designed to help answer the following questions:
- What is the water quality of our Nation’s streams, rivers, and groundwater?
- How are water-quality conditions changing over time?
The U.S. Geological Survey (USGS) NWQN was formed in 2013 to develop long-term consistent and comparable information in support of national, regional, state, and local information needs related to water-quality management and policy. Sampling of both surface water and groundwater sites within this network date back to the early 1990’s when many sites were part of the National Water Quality Assessment (NAWQA) Project. At the beginning of the third decade (2013-2022) of the NAWQA Project, sites from NAWQA, the National Stream Quality Accounting Network (NASQAN), the National Monitoring Network (NMN), and the Hydrologic Benchmark Network (HBN) with historical streamflow and water-quality data were selected for inclusion in the NWQN for surface water sampling. When the NAWQA project ended in 2022, the groundwater trend networks became a part of the NWQN and will continue to be sampled.
As of 2025, the NWQN consists of 102 surface water (streams and rivers) and 258 groundwater sampling locations throughout the United States. Water-quality data are collected and analyzed using consistent methods to enable comparative assessments of water quality across the Nation and through time. Methods of sample collection used by the NWQN conform to the USGS National Field Manual for the Collection of Water-Quality Data. Surface water sites are typically sampled between 12 and 20 times per year, depending on site type. In addition to discrete surface-water quality sampling, the NWQN also supports continuous water-quality monitoring at twelve river sites and continuous water temperature at most of the small minimally disturbed reference sites. Groundwater sites are sampled once every 10 years. The longer time interval is acceptable because groundwater quality changes more slowly than surface-water quality. The scientific data are used by national, regional, state, and local agencies to develop science-based policies and management strategies to improve and protect water resources used for drinking water, recreation, irrigation, energy development, and ecosystem needs.
Groundwater and surface water are often interconnected and can be used for the same purposes, including as a source for drinking water or irrigation. Additionally, since groundwater and surface water can flow into each other, water quality in groundwater and surface water can be directly connected. Therefore, samples and monitoring at groundwater and surface water sites often cover the same parameters.
What USGS measures
| Parameters measured on site include: | Parameters measured in the laboratory include: |
| temperature | nutrients |
| specific conductance | major ions |
| dissolved oxygen | pesticides (one third of groundwater sites and non-reference surface water sites) |
| pH | Per- and Polyfluoroalkyl Substances (PFAS) (all groundwater and subset of surface water sites) |
| turbidity | tritium (an age tracer) (groundwater only) |
| radionuclides (groundwater public and domestic supply wells only) | |
| suspended sediment (surface water only) | |
| microbiological contaminants (groundwater public and domestic supply wells only) | |
| volatile organic compounds (VOCs) (one third of groundwater sites) |
Access NWQN data and information
Data from the USGS National Water Quality Network can be accessed through the USGS Water Data for the Nation website and web services.
Surface water quality
Surface water data collected as part of the NWQN is used in a national context to describe water quality characteristics of rivers and streams influenced by various land uses (for example, urban and agricultural land use), compared to minimally disturbed reference sites. The NWQN is the only nationally designed, long-term monitoring network for tracking the quality of rivers and streams with consistent, comparable data collection and analytical methods at all sites. When paired with context of streamflow conditions and landscape characteristics, the data from the NWQN provides important information on the amount of various water-quality constituents moving through rivers to receiving waters, how water-quality concentrations and loads are changing through time, and how certain key pollutant concentrations, such as pesticides and PFAS, compare to relevant human health and aquatic-life benchmarks, which is critical information to guide decisions that seek to preserve the health of humans and aquatic life. The importance of aquatic life and their habitats is not only critical to preserving ecosystems Nationwide, but also the benefits those ecosystems provide to society. Analysis of these data are also critical in determining how successful implemented pollution control measures are at improving water-quality in streams, rivers and receiving waters.
Sites prioritized for continued monitoring through the NWQN include sites upstream from key receiving waters, sites with long-term historical records, and sites that improve network representation of different geographic and land-use settings. The primary objectives are to determine the status and trends of concentrations and loads of contaminants, nutrients, and sediment to the Nation’s large rivers, loads to selected major estuaries; and to determine the status and trends in concentrations of contaminants, nutrients, and sediment for wadeable streams in selected land-use and environmental settings.
Water-Quality Changes in the Nation's Streams and Rivers is an online graphical data tool that provides annual summaries of stream trends in nutrient and sediment concentrations.
Groundwater quality
Groundwater data collected through NWQN provide information on the quality of water in shallow monitoring wells, domestic-supply wells, and in some cases public-supply wells. Groundwater data can be used by our partners to help understand the quality and availability of water for drinking water, irrigation, livestock, and other uses, and how that is changing over time. The NWQN, consists of 80 regional trend groundwater networks and 22 public supply groundwater networks. Each of the 80 regional trends networks is sampled on a rotating basis every 10 years - about 8 regional networks are sampled each year. The 80 regional trend networks are designed to monitor shallow groundwater underlying agricultural or urban land use, or the aquifer depth zone used for domestic (homeowner) supply, but do not cover the depth zone used for public supply. The 22 public supply networks cover the aquifer depth zone used for public water supply. These public supply networks are not part of the regional trend networks and have only been sampled once previously (2012-2019). To cover this part of the resource, public supply networks are being resampled for PFAS as funds become available. The 22 public supply networks sampled by USGS represent 84% of the groundwater used for public supply in the Nation. In 2024, there were 2,114 groundwater monitoring sites in the entire NWQN trends network, with 228 being sampled in 2024 and 30 supplemental wells being sampled to characterize PFAS in public supply wells.
The Decadal Change in Groundwater Quality web application shows how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.
Connecting the dots between USGS water monitoring networks
The NWQN is the water-quality arm of the USGS national water monitoring “network of networks” that measures the Nation’s water resources to meet the water management and prediction needs of the Nation. Data from the NWQN is also used in the USGS National Water Availability Assessment Report which provides a comprehensive, scientific summary and interpretation of water quality, quantity and water use in the United States. This effort draws upon data collected at stream sampling sites, groundwater wells, rain gages and other monitoring locations maintained by the USGS. In some cases, this information is interpreted directly in support of the National Assessment and in other cases serves as calibration data for regional and national-scale models of key hydrologic processes in the United States.
The funding for the NWQN comes from the National Water Quality Program (NWQP). The USGS Observing Systems Division within the Water Resources Mission Area operates and coordinates large, congressionally mandated USGS water-observing networks such as the National Water Quality Network.
Authorizations
USGS activities are conducted under the authority of various pieces of authorizing federal legislation. The following is a subset of authorizations that are related to the National Water Quality Network:
53 U.S.C. § 4001 | Harmful Algal Blooms and Hypoxia Research and Control Act of 1998, as amended (Pub. L. 113-124)
Names DOI as one of the Interagency Task Force members. Members are directed to "support the implementation of the Action Strategy, including the coordination and integration of the research of all Federal programs". Under this authority, the USGS is an active member agency in the Interagency Working Group on Harmful Algal Blooms and Hypoxia Research and Control Act (HABHRCA). USGS scientists have been leaders in the development of two published research plans and action strategies for Congress on harmful algal blooms (HABs) and hypoxia: a comprehensive strategy for the entire U.S. and a more targeted strategy for the Great Lakes. In addition, USGS monitoring, assessment, research, and modeling activities on HABs and hypoxia contribute toward successful implementation of the action plans and strategies recommended both HABHRCA reports.
33 U.S.C. § 652 | Upper Mississippi River Management Act of 1986
Authorizes a program for planning, construction, and evaluation of measures for fish and wildlife habitat rehabilitation and enhancement; cooperative effort and mutual assistance for use, protection, growth, and development of the Upper Mississippi River system; implementation of a long-term resource monitoring program; and applied research program, including research on water quality issues affecting the Mississippi River (including elevated nutrient levels) and the development of remediation strategies. Under this authority, the USGS monitors nutrients loads and other water-quality constituents in the Mississippi River Basin and other large watersheds that drain into other important coastal areas and the Great Lakes, conducts research on nutrient cycling, and completes studies and develops water-quality models that can be used to assess and implement best management practices in agriculture and urban settings.
33 U.S.C. 1251 et seq. | Federal Water Pollution Control Act Amendments of 1972 (and its successors, the Clean Water Act of 1977 and the Water Quality Act of 1987)
Authorizes extensive water quality planning, studies, and monitoring under the direction primarily of the Environmental Protection Agency (EPA). The USGS is called upon to participate in many of these activities, partly by EPA and partly by State agencies in the Federal-State Cooperative Program. The act of 1987 includes new water quality work concerning Chesapeake Bay, the Great Lakes, Estuary and Clean Lakes Programs, and studies of water pollution problems in aquifers. Estuaries and Clean Waters Act of 2000 amends the Federal Water Pollution and Control Act (commonly known as the Clean Water Act) to include authorization for the following: Title I, Estuary Restoration; Title II, Chesapeake Bay Restoration; Title III, National Estuary Program; Title IV, Long Island Sound Restoration; Title V, Lake Pontchartrain Basin Restoration; Title VI, Alternative Water Sources; Title VII, Clean Lakes; and Title VIII, Tijuana River Valley Estuary and Beach Cleanup. The Clean Water Act charges States and Tribes with setting specific water-quality criteria appropriate for their waters and for developing pollution control programs to meet the criteria. The USGS provides nationally consistent monitoring and hydrologic data that are used by States and Tribes as they strive to meet Clean Water Act requirements. The USGS also is a key Federal partner in both the Chesapeake Bay Program and the National Estuary Program.
42 U.S.C. § 10367 - 10368 | Omnibus Public Land Management Act of 2009 (SECURE Water Act) (Pub. L. 111-11)
Authorizes (Title IX, Subtitle F, Sec. 9507 and 9508) the implementation of the national streamflow information program (more than 4,700 federal priority streamgages), development of a systematic groundwater monitoring program for each major aquifer system (the National Groundwater Monitoring Network), completion of a national brackish groundwater assessment, and implementation of the national water availability and use assessment program.
The subsequent reauthorization of the SECURE Water Act: Public Law 118-174.
National Defense Authorization Act for Fiscal Year 2020. (Pub. L. 116-92)
(a) IN GENERAL. —The (USGS) Director shall carry out a nationwide sampling to determine the concentration of highly fluorinated compounds (commonly referred to as PFAS) in estuaries, lakes, streams, springs, wells, wetlands, rivers, aquifers, and soil using the performance standard developed under section 7332(a).
Here is a full list of National Water Quality Program authorizations.
Below are other science topics and efforts related to the National Water Quality Network.
National Water Monitoring Network
USGS National Streamgaging Network
National Water-Quality Assessment (NAWQA)
Understanding the quality of U.S. streams, rivers, and groundwater requires consistent data collection and analysis over decades for proper context of current conditions. The USGS collects nationally standardized data and information as part of the National Water Quality Network (NWQN). The NQWN is made up of sites across the Nation where USGS scientists regularly measure water-quality conditions.
The National Water Quality Network (NWQN) is designed to help answer the following questions:
- What is the water quality of our Nation’s streams, rivers, and groundwater?
- How are water-quality conditions changing over time?
The U.S. Geological Survey (USGS) NWQN was formed in 2013 to develop long-term consistent and comparable information in support of national, regional, state, and local information needs related to water-quality management and policy. Sampling of both surface water and groundwater sites within this network date back to the early 1990’s when many sites were part of the National Water Quality Assessment (NAWQA) Project. At the beginning of the third decade (2013-2022) of the NAWQA Project, sites from NAWQA, the National Stream Quality Accounting Network (NASQAN), the National Monitoring Network (NMN), and the Hydrologic Benchmark Network (HBN) with historical streamflow and water-quality data were selected for inclusion in the NWQN for surface water sampling. When the NAWQA project ended in 2022, the groundwater trend networks became a part of the NWQN and will continue to be sampled.
As of 2025, the NWQN consists of 102 surface water (streams and rivers) and 258 groundwater sampling locations throughout the United States. Water-quality data are collected and analyzed using consistent methods to enable comparative assessments of water quality across the Nation and through time. Methods of sample collection used by the NWQN conform to the USGS National Field Manual for the Collection of Water-Quality Data. Surface water sites are typically sampled between 12 and 20 times per year, depending on site type. In addition to discrete surface-water quality sampling, the NWQN also supports continuous water-quality monitoring at twelve river sites and continuous water temperature at most of the small minimally disturbed reference sites. Groundwater sites are sampled once every 10 years. The longer time interval is acceptable because groundwater quality changes more slowly than surface-water quality. The scientific data are used by national, regional, state, and local agencies to develop science-based policies and management strategies to improve and protect water resources used for drinking water, recreation, irrigation, energy development, and ecosystem needs.
Groundwater and surface water are often interconnected and can be used for the same purposes, including as a source for drinking water or irrigation. Additionally, since groundwater and surface water can flow into each other, water quality in groundwater and surface water can be directly connected. Therefore, samples and monitoring at groundwater and surface water sites often cover the same parameters.
What USGS measures
| Parameters measured on site include: | Parameters measured in the laboratory include: |
| temperature | nutrients |
| specific conductance | major ions |
| dissolved oxygen | pesticides (one third of groundwater sites and non-reference surface water sites) |
| pH | Per- and Polyfluoroalkyl Substances (PFAS) (all groundwater and subset of surface water sites) |
| turbidity | tritium (an age tracer) (groundwater only) |
| radionuclides (groundwater public and domestic supply wells only) | |
| suspended sediment (surface water only) | |
| microbiological contaminants (groundwater public and domestic supply wells only) | |
| volatile organic compounds (VOCs) (one third of groundwater sites) |
Access NWQN data and information
Data from the USGS National Water Quality Network can be accessed through the USGS Water Data for the Nation website and web services.
Surface water quality
Surface water data collected as part of the NWQN is used in a national context to describe water quality characteristics of rivers and streams influenced by various land uses (for example, urban and agricultural land use), compared to minimally disturbed reference sites. The NWQN is the only nationally designed, long-term monitoring network for tracking the quality of rivers and streams with consistent, comparable data collection and analytical methods at all sites. When paired with context of streamflow conditions and landscape characteristics, the data from the NWQN provides important information on the amount of various water-quality constituents moving through rivers to receiving waters, how water-quality concentrations and loads are changing through time, and how certain key pollutant concentrations, such as pesticides and PFAS, compare to relevant human health and aquatic-life benchmarks, which is critical information to guide decisions that seek to preserve the health of humans and aquatic life. The importance of aquatic life and their habitats is not only critical to preserving ecosystems Nationwide, but also the benefits those ecosystems provide to society. Analysis of these data are also critical in determining how successful implemented pollution control measures are at improving water-quality in streams, rivers and receiving waters.
Sites prioritized for continued monitoring through the NWQN include sites upstream from key receiving waters, sites with long-term historical records, and sites that improve network representation of different geographic and land-use settings. The primary objectives are to determine the status and trends of concentrations and loads of contaminants, nutrients, and sediment to the Nation’s large rivers, loads to selected major estuaries; and to determine the status and trends in concentrations of contaminants, nutrients, and sediment for wadeable streams in selected land-use and environmental settings.
Water-Quality Changes in the Nation's Streams and Rivers is an online graphical data tool that provides annual summaries of stream trends in nutrient and sediment concentrations.
Groundwater quality
Groundwater data collected through NWQN provide information on the quality of water in shallow monitoring wells, domestic-supply wells, and in some cases public-supply wells. Groundwater data can be used by our partners to help understand the quality and availability of water for drinking water, irrigation, livestock, and other uses, and how that is changing over time. The NWQN, consists of 80 regional trend groundwater networks and 22 public supply groundwater networks. Each of the 80 regional trends networks is sampled on a rotating basis every 10 years - about 8 regional networks are sampled each year. The 80 regional trend networks are designed to monitor shallow groundwater underlying agricultural or urban land use, or the aquifer depth zone used for domestic (homeowner) supply, but do not cover the depth zone used for public supply. The 22 public supply networks cover the aquifer depth zone used for public water supply. These public supply networks are not part of the regional trend networks and have only been sampled once previously (2012-2019). To cover this part of the resource, public supply networks are being resampled for PFAS as funds become available. The 22 public supply networks sampled by USGS represent 84% of the groundwater used for public supply in the Nation. In 2024, there were 2,114 groundwater monitoring sites in the entire NWQN trends network, with 228 being sampled in 2024 and 30 supplemental wells being sampled to characterize PFAS in public supply wells.
The Decadal Change in Groundwater Quality web application shows how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.
Connecting the dots between USGS water monitoring networks
The NWQN is the water-quality arm of the USGS national water monitoring “network of networks” that measures the Nation’s water resources to meet the water management and prediction needs of the Nation. Data from the NWQN is also used in the USGS National Water Availability Assessment Report which provides a comprehensive, scientific summary and interpretation of water quality, quantity and water use in the United States. This effort draws upon data collected at stream sampling sites, groundwater wells, rain gages and other monitoring locations maintained by the USGS. In some cases, this information is interpreted directly in support of the National Assessment and in other cases serves as calibration data for regional and national-scale models of key hydrologic processes in the United States.
The funding for the NWQN comes from the National Water Quality Program (NWQP). The USGS Observing Systems Division within the Water Resources Mission Area operates and coordinates large, congressionally mandated USGS water-observing networks such as the National Water Quality Network.
Authorizations
USGS activities are conducted under the authority of various pieces of authorizing federal legislation. The following is a subset of authorizations that are related to the National Water Quality Network:
53 U.S.C. § 4001 | Harmful Algal Blooms and Hypoxia Research and Control Act of 1998, as amended (Pub. L. 113-124)
Names DOI as one of the Interagency Task Force members. Members are directed to "support the implementation of the Action Strategy, including the coordination and integration of the research of all Federal programs". Under this authority, the USGS is an active member agency in the Interagency Working Group on Harmful Algal Blooms and Hypoxia Research and Control Act (HABHRCA). USGS scientists have been leaders in the development of two published research plans and action strategies for Congress on harmful algal blooms (HABs) and hypoxia: a comprehensive strategy for the entire U.S. and a more targeted strategy for the Great Lakes. In addition, USGS monitoring, assessment, research, and modeling activities on HABs and hypoxia contribute toward successful implementation of the action plans and strategies recommended both HABHRCA reports.
33 U.S.C. § 652 | Upper Mississippi River Management Act of 1986
Authorizes a program for planning, construction, and evaluation of measures for fish and wildlife habitat rehabilitation and enhancement; cooperative effort and mutual assistance for use, protection, growth, and development of the Upper Mississippi River system; implementation of a long-term resource monitoring program; and applied research program, including research on water quality issues affecting the Mississippi River (including elevated nutrient levels) and the development of remediation strategies. Under this authority, the USGS monitors nutrients loads and other water-quality constituents in the Mississippi River Basin and other large watersheds that drain into other important coastal areas and the Great Lakes, conducts research on nutrient cycling, and completes studies and develops water-quality models that can be used to assess and implement best management practices in agriculture and urban settings.
33 U.S.C. 1251 et seq. | Federal Water Pollution Control Act Amendments of 1972 (and its successors, the Clean Water Act of 1977 and the Water Quality Act of 1987)
Authorizes extensive water quality planning, studies, and monitoring under the direction primarily of the Environmental Protection Agency (EPA). The USGS is called upon to participate in many of these activities, partly by EPA and partly by State agencies in the Federal-State Cooperative Program. The act of 1987 includes new water quality work concerning Chesapeake Bay, the Great Lakes, Estuary and Clean Lakes Programs, and studies of water pollution problems in aquifers. Estuaries and Clean Waters Act of 2000 amends the Federal Water Pollution and Control Act (commonly known as the Clean Water Act) to include authorization for the following: Title I, Estuary Restoration; Title II, Chesapeake Bay Restoration; Title III, National Estuary Program; Title IV, Long Island Sound Restoration; Title V, Lake Pontchartrain Basin Restoration; Title VI, Alternative Water Sources; Title VII, Clean Lakes; and Title VIII, Tijuana River Valley Estuary and Beach Cleanup. The Clean Water Act charges States and Tribes with setting specific water-quality criteria appropriate for their waters and for developing pollution control programs to meet the criteria. The USGS provides nationally consistent monitoring and hydrologic data that are used by States and Tribes as they strive to meet Clean Water Act requirements. The USGS also is a key Federal partner in both the Chesapeake Bay Program and the National Estuary Program.
42 U.S.C. § 10367 - 10368 | Omnibus Public Land Management Act of 2009 (SECURE Water Act) (Pub. L. 111-11)
Authorizes (Title IX, Subtitle F, Sec. 9507 and 9508) the implementation of the national streamflow information program (more than 4,700 federal priority streamgages), development of a systematic groundwater monitoring program for each major aquifer system (the National Groundwater Monitoring Network), completion of a national brackish groundwater assessment, and implementation of the national water availability and use assessment program.
The subsequent reauthorization of the SECURE Water Act: Public Law 118-174.
National Defense Authorization Act for Fiscal Year 2020. (Pub. L. 116-92)
(a) IN GENERAL. —The (USGS) Director shall carry out a nationwide sampling to determine the concentration of highly fluorinated compounds (commonly referred to as PFAS) in estuaries, lakes, streams, springs, wells, wetlands, rivers, aquifers, and soil using the performance standard developed under section 7332(a).
Here is a full list of National Water Quality Program authorizations.
Below are other science topics and efforts related to the National Water Quality Network.