U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2013–3008

February 2013

National Water-Quality Assessment Program

Water Quality Remains a Concern for Human Use and Ecosystem Health

Water-quality issues facing the Nation are growing in number and complexity, and solutions 

are becoming more challenging and costly. The U.S. Census Bureau projects that our population will 

increase 25 percent by 2050, to almost 400 million people. Increases in population will be accompanied by development of land for urban and other non-agricultural uses, increased use of fertilizers and 

pesticides for food production, and greater pressure on existing resources to supply water for energy 

development, irrigation, drinking water, and ecosystem needs. These factors, alone or in combination, 

may degrade stream and coastal ecosystems and the quality of drinking water supplies if not effectively managed. Key issues we already know about include:

•	 Contaminants in Streams and Groundwater—Eighty percent of streams in urban areas were 

found to have at least one pesticide that exceeded criteria set to protect aquatic life (Gilliom and 

others, 2006). Of our public and domestic wells―which supply drinking water to over 150 million 

people―more than 20 percent contain at least one contaminant at levels of potential health concern (DeSimone and others, 2009; Toccalino and Hopple, 2010).

•	 Degraded Stream Health—Forty-two percent of wadeable stream miles in the United States are 

in poor or degraded condition (U.S Environmental Protection Agency, 2006). Widespread causes 

include excess nutrients and sediment, habitat disturbance, and altered streamflow. Minimum 

and maximum stream flows were found to be altered by human activities at 86 percent of almost 

3,000 streams assessed across the Nation, and the likelihood of biological impairment increased 

with the severity of flow alteration (Carlisle and others, 2010).

•	 Changing Stream and Groundwater Quality—Despite major efforts to reduce sources of nitrogen 

and phosphorus contaminating streams and rivers, analysis of trends in concentrations from about 

1993 to 2003 show minimal changes at the majority of sites monitored, although most sites with 

significant change show nutrient concentrations increasing. During the same period, the percentage 

of wells with nitrate concentrations greater than the drinking water standard increased from 16 to 

21 percent (Dubrovsky and others, 2010).

•	 Deteriorating Estuary Conditions—Almost two-thirds of the Nation’s major estuaries are 

degraded by excess nutrients, which cause “dead zones” (areas of low dissolved oxygen) that 

threaten economically important fisheries. The spread of dead zones is projected to worsen through 

2020 in 48 of these estuaries as population growth, agriculture, and other development increase the 

amount of nutrients flowing into coastal waters (Diaz and Rosenberg, 2008).

Twenty-one years ago, Congress established the National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey 

(USGS) to answer a fundamental question:

What is the status of the Nation’s water quality, and is it getting better or worse?

Since then, NAWQA has been a primary source of nationally consistent data and information on the quality of the Nation’s streams and 

groundwater. Objective and nationally-consistent water-quality data and models provide answers to where, when, and why the Nation’s water 

quality is degraded and what can be done to improve and protect it for human and ecosystem needs. During its first decade (1991–2001), 

NAWQA focused on establishing a nationally consistent water-quality dataset that could serve as a baseline for trend evaluation, modeling 

efforts, and research studies. During its second decade (2002–2012), the NAWQA program built upon the baseline investigations by reporting 

on how water-quality conditions changed over time and by developing regional-scale water-quality models to extrapolate findings to unsampled 

areas and model-based tools that resource managers can use to evaluate the likely consequences of different management practices or policy 

scenarios. Water-quality data, models, and scientific knowledge generated by NAWQA are used by national, regional, State, and local agencies 

to develop more effective, science-based policies and strategies for protecting and managing water quality and aquatic ecosystems. Information 

produced by NAWQA over the past 21 years also provides the foundation for addressing current and future water-quality issues.

Photograph by Alan Cressler, 

U.S. Geological Survey

Tracking and Forecasting the Nation’s Water Quality

Priorities and Strategies for 2013–2023

The need for a national 

water quality assessment is 

as important, if not more so 

today, as when the NAWQA 

program was established.

—National Research Council 

(2012, p. 5)

Printed on recycled paper
Urban streams

Agricultural streams

Undeveloped streams

Large inland rivers

Large coastal rivers

EXPLANATION

Investments in Monitoring and Modeling Are Needed to Address Current and Future Challenges

For NAWQA’s third decade (2013–2023), a new strategic Science Plan has been developed that describes a 10-year strategy for 

building upon and enhancing assessment of the Nation’s freshwater quality and aquatic ecosystems. The plan continues strategies that 

have been central to NAWQA’s long-term success, but it also adjusts the monitoring design, data analysis, and reporting to address 

monitoring and science information needs identified by NAWQA stakeholders and the National Research Council (2012). Meeting 

stakeholder needs for more timely reporting of water-quality information and development of decision-support tools are key components of the plan. Example products include (1) annual Web-based reporting of the concentrations, loads, and trends of nutrients, 

sediment, and other contaminants in rivers flowing into important coastal estuaries; (2) maps showing the distributions of nitrate and 

arsenic in water-supply aquifers at the depths pumped by domestic or public-supply wells, and (3) model-based decision-support tools 

that allow managers to evaluate how water-quality or ecosystem condition may change in response to different scenarios of population 

growth, climate change, or land-use management.

Monitoring and Modeling Activities To Begin in Fiscal Year 2013

Restoring and enhancing monitoring networks, particularly for surface water, and expanding development of NAWQA modeling tools were the highest priorities of stakeholders and the National Research Council (2012). An overview of surface-water and 

groundwater monitoring and modeling activities that will be started in fiscal year 2013 (FY13) shows how these broad approaches 

will be used to assess specific water-quality issues with available funding.

Surface-Water Monitoring and Modeling

The NAWQA strategy will continue to focus on assessing 

nutrient, sediment, and contaminant concentrations and transport 

in rivers and streams in major river basins throughout the Nation, 

particularly the Mississippi River basin, and also watersheds of 

critical estuaries such as Chesapeake Bay and San Francisco Bay. 

Water-quality models that estimate nutrient and sediment loads 

(SPARROW models; Schwarz and others, 2006) and pesticide 

concentrations in streams (WARP models; Stone and Gilliom, 

2009) will be updated and enhanced in four regions of the country—the Mississippi River basin and rivers draining the northeast, 

southeast, and west—as well as for the national scale. Planned 

enhancements include increased temporal resolution (shorter 

time scale), updated contaminant source data, and simulation of 

seasonal to annual variations in streamflow, contaminant concentrations, and loads. The improved models will be used to develop 

more effective decision-support tools to forecast how nutrient and 

sediment loads will change in response to changes in climate, land 

use, or management practices.

NAWQA has evolved from a water quality program emphasizing data collection 

and trend assessments to one that has the potential to predict and forecast pollutant 

occurrence and trends under multiple scenarios at nationally significant scales.

—National Research Council (2012, p. 158)

Figure 1. Beginning in fiscal year 2013, NAWQA will monitor 100 stream and river sites every year. 
EXPLANATION

50 percent

25 percent

15 percent

5 percent 

Principal aquifers selected for assessment 

 and percent of water provided for 

 public supply 

Groundwater trend networks

Major aquifer study (32)

Agricultural land use study (27)

Urban land use study (20)

Glacial aquifer 

Northern Atlantic

Coastal Plain

aquifer

Coastal Lowlands

aquifer

Central Valley

aquifer

Water-quality monitoring in FY13 will be done at a network of 

100 sites (fig. 1), most of which are long-term USGS monitoring sites that 

have more than 20 years of data. The national network includes 61 large 

river sites that will provide basic coverage of large-scale trends in nutrient, 

sediment, and contaminant loading to inland or coastal receiving waters, 

and 39 wadeable stream sites that will be used to track trends in waterquality and ecosystem condition at urban, agricultural, and undeveloped 

watersheds selected to represent the national diversity of environmental 

settings. Most sites will be sampled 12 to 18 times per year for a wide 

range of contaminants. Continuous monitoring of key water properties, 

including salinity, nitrate and turbidity, will start at 5 sites equipped with 

state-of-the-art water-quality sensors. These data will improve estimates 

of nutrient and sediment loads, and the continuous water-quality data 

will be incorporated into water-quality models. At the 39 wadeable stream 

sites, evaluations of the condition of algal, macroinvertebrate, and fish 

communities will be conducted annually.

Groundwater Monitoring and Modeling

NAWQA is the only Federal program that assesses the status of 

the Nation’s groundwater quality and reports on how these conditions 

are changing over time. Groundwater studies are planned in 20 principal aquifers, which collectively account for more than 75 percent of the 

national groundwater used for drinking water (fig. 2). Statistical models 

and monitoring data will be combined to generate maps of selected contaminant occurrence at the depth zones used for domestic and public supply. 

In four principal aquifers—the Central Valley of California, the Coastal 

Lowlands of the lower Gulf Coast states, the Glacial, and the Northern 

Atlantic Coastal Plain—groundwater-quality data will be combined with 

groundwater flow models to provide a three-dimensional estimate of the 

amount of groundwater available in each aquifer, its vulnerability to contaminants derived from natural and (or) human sources, and an understanding of how groundwater quality may respond to changes in climate, land 

use, and water use over time.

About 2,500 wells, distributed among 79 existing networks, will be 

resampled over the next decade for key water properties, nitrate, and trace 

elements (fig. 2) to assess how shallow groundwater quality is changing beneath urban and agricultural lands and in deeper domestic wells. 

Subsets of wells in selected networks will also be sampled for pesticides, 

contaminants of emerging concern (pharmaceuticals, hormones, and high 

production volume chemicals), radiochemicals, microbial contaminants, 

and tracers that indicate the approximate age of the groundwater. About 

1,500 deep public supply wells will be sampled in the next decade to help 

characterize water-quality conditions in parts of the aquifers that were 

not examined in previous decades; remaining samples will be collected 

from domestic wells and shallow monitoring wells underlying urban 

and agricultural areas.

The California State Water Resources Control Board has worked closely with the U.S. Geological Survey to develop a 

comprehensive monitoring and assessment program for California’s groundwater basins. The approach, methods, and results 

from NAWQA studies have been fully integrated into California’s plans to evaluate groundwater quality on a statewide basis.

—Arthur G. Baggett, Jr., State Water Resources Control Board

Figure 2. Seventy-nine NAWQA well networks in 20 principal aquifers will be resampled to assess decadal-scale 

trends in groundwater quality. Each groundwater trend network consists of 25 to 30 wells in a principal aquifer, 

distributed randomly across areas ranging from several hundred to several thousand square miles. Seven or 

eight trend networks will be resampled in fiscal year 2013; a similar number of networks will be resampled in each 

subsequent year of the decade.
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Year

Concentration of diazinon, 

in micrograms per liter

0.0001

0.001

0.01

0.1

1

Phase-out 

of indoor 

residential

use of diazinon

Phase-out 

of outdoor 

residential

use of diazinon

U.S. Environmental Protection Agency

Aquatic Life Criterion

Accotink Creek

EXPLANATION

Measured diazinon concentration

Nondetection

Simulated diazinon concentration

Trend

0 250 500 MILES

0 250 500 KILOMETERS

Predicted nitrate concentration, in milligrams per liter

EXPLANATION

Less than or equal to 1

Greater than 1 to 5 Missing data

Greater than 10

Greater than 5 to 10

Products Designed to Meet the Nation’s Water-Quality Information Needs

The NAWQA program’s third decade will yield advances in water-quality information and science that can markedly improve the effectiveness of water-quality policies and management decisions. Examples of the types of data and information products planned for the next decade are 

described below.

Restoring Monitoring for Reliable and Timely Status and Trend Assessments

The NAWQA program will work with State and Federal partners 

to fill monitoring gaps in critical watersheds and aquifers by leveraging 

available resources and collaborating with other programs to build an 

expanded and sustainable national network. Monitoring approaches will 

emphasize rapid feedback on changing water-quality conditions so that 

managers can identify emerging problems, develop effective responses, 

and evaluate the performance of management strategies. Recent 

analyses of water-quality trends have shown that monitoring must be 

frequent and sustained every year to reliably detect trends at the time 

scales at which important changes in contaminant sources and management strategies occur. Therefore, the Science Plan emphasizes returning to yearly intensive monitoring of sites that are part of NAWQA’s 

surface-water-quality network, rather than a rotational approach with 

many sites only periodically monitored.

For example, monitoring data for Accotink Creek, a small urban 

stream near Washington, D.C., shows the importance of frequent 

sampling to detect and quantify the decline in stream concentrations of 

diazinon that occurred following the phase-out of the residential use of 

this insecticide that began in 2000. Being able to document the effectiveness of water-quality improvement strategies in a timely manner, 

as demonstrated by the every-year monitoring approach used in this 

example, is vital to regulatory agencies and other stakeholders in order 

to track the performance of management practices and determine implications for future strategies.

The products and studies produced by the USGS are beyond reproach and represent an independent 

scientific voice that water planners look to for guidance.

—Dave Kanzer, Senior Water Resources Engineer, Colorado River Water Conservation District

Transforming Data and Models into Tools for Decisionmakers

The NAWQA program’s water-quality models quantitatively link 

sources and management practices to water-quality benefits and effects 

and can do so at multiple hydrologic scales—from headwater streams 

to rivers flowing into estuaries, and from shallow groundwater to 

deep regional aquifers. In the first two decades of NAWQA, progress 

was made on the application of models to evaluate the vulnerability 

of streams and groundwater to selected contaminants, such as nitrate. 

Progress was also made on the application of models that link causal 

factors and individual contaminants at regional and national scales.

Findings from a national nitrate model for shallow groundwater 

(Nolan and Hitt, 2006) illustrate the type of information that will be 

further refined as data and information on sources of contaminants, 

management practices, and other important factors improve. Such models can be developed for other contaminants—dissolved solids, arsenic, 

and pesticides—and for specific regions of the country. They provide 

resource managers with an important starting point for evaluating 

which aquifers or streams are likely to have contaminant concentrations 

high enough to impair drinking water supplies or threaten the health of 

aquatic organisms. Other models examine how groundwater interacts 

with surface water to affect contaminant transport and the amount of 

time it takes water and contaminants to move from the land surface, 

through aquifers, and then to streams. The resulting modeling tools 

can be used by resource managers to evaluate changes in water quality 

caused by different management practices or regulatory policies and 

how long it will take for the effects of those changes to be observed in 

their watershed or aquifer.
GULF OF

MEXICO

ATLANTIC

OCEAN

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25

20

15

10

5

0

Percent decrease

How will a 50 percent decrease in agricultural nitrogen

inputs change nutrient loads to eutrophic estuaries in the Southeast? 

EXPLANATION

Eutrophic estuary (Bricker and others, 1999)

Agricultural land use in watersheds of 

 eutrophic estuaries

Percent 

of sites

modified

50

40

30

20

10

0

Depleted

Inflated

Unaltered

Arid

Wet

EXPLANATION

High

Low

EXPLANATION

Predicted

concentrations 

of atrazine

High

Low

EXPLANATION

Providing Data and Tools to Predict Ecological Condition in Streams

Targeted regional studies will provide resource managers with data and tools to understand and predict ecological conditions in relation to streamflow alteration and concentrations of 

contaminants, nutrients, and sediment. New national and regional models of potential stressors, 

such as altered streamflow, nutrient delivery, and contaminant toxicity, will provide managers 

with critical information on stressors that affect ecological health. For example, Carlisle and others 

(2010) showed that streams that had altered streamflows had fewer sensitive fish species than 

streams characterized by more natural flow regimes.

The regional studies will provide detailed understanding of how natural and human factors 

affect water quality and ecological conditions in major regions of the Nation, improve understanding of how stream quality will respond to management scenarios, and provide information that 

facilitates investment in the most effective restoration strategies. The first of these regional assessments is being developed in collaboration with the States and the U.S. Environmental Protection 

Agency’s National Rivers and Streams Assessment program and will focus on stream quality in 

the agricultural Midwest, a region encompassing parts of 12 states (U.S. Geological Survey, 2012). 

Other regional studies may be done in the humid southeast, arid southwest, the Atlantic Highlands, 

and the Rocky Mountains.

This USGS SPARROW Model decision support system represents a major advance in the availability of sound scientific 

information to enable the effective management of this growing threat to our valued coastal resources and economies.

—Dr. Robert Magnien, Director of the Center for Sponsored Coastal Ocean Research, 

National Oceanic and Atmospheric Administration

Forecasting Future Conditions and Testing Policy Scenarios

Forecasting and scenario-testing tools—an array of statistical and simulation models—developed by NAWQA will enable timely evaluation of current 

water-quality issues as well as the possible effects of future scenarios of changing climate, land use, and management practices. Enhanced versions of the 

SPARROW model, as well as other water-quality models, will be converted into 

Web-accessible tools that managers can use to evaluate how water quality and 

aquatic ecosystems may change in response to different scenarios.

For example, SPARROW was used to predict how a 50-percent reduction in agricultural nitrogen inputs would decrease loadings to eutrophic 

estuaries in the eastern Gulf of Mexico and the South Atlantic Coastal Plain 

(Hoos and McMahon, 2009). The model showed that resulting nitrogen 

loads to estuaries would decrease from as little as 5 percent to a maximum of 

24 percent, indicating that—in terms of total annual nitrogen load—reduction 

of agricultural sources alone may not markedly improve eutrophication in 

some of these estuaries.

Similarly, coupled groundwater quality and flow models will enable water 

managers to evaluate the amount of time it may take for contaminated shallow 

groundwater to reach production zones used as drinking water supplies.

The [NAWQA] program has translated and interpreted its high-quality, nationally consistent data with sophisticated 

tools so that policy and decision makers can use the program’s science to inform efficient decision-making.

—National Research Council (2012, p. 7)

Altered Streamflow

Nutrient Delivery

Contaminant Toxicity
Major rivers Sites or networks to be monitored Sites or networks that will not be monitored Principal aquifers selected for assessment

EXPLANATION

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Surface-water monitoring sites Groundwater trend network sites

Start-up Phase of the Science Plan

Anticipated funding for fiscal year 2013—approximately 25 percent of that needed to fully implement the recommended Science Plan—will 

support a scaled-back start-up phase of the science strategy endorsed by stakeholders and the National Research Council (fig. 3). A combination 

of funding growth and extensive collaboration with Federal, State, and local agencies, public interest groups, professional and trade associations, 

academia, and private industry will be needed to fully realize the monitoring and modeling goals laid out in the Science Plan. Partnering with other 

USGS programs is also important to the success of NAWQA in the coming decade. Collaborative efforts are being planned with the Water Census 

Program, Groundwater Resources Program, and the Cooperative Water Program on various data collection and modeling activities. These external 

and internal partnerships will increase geographic and temporal coverage through integration of multiple data sources and improve our ability to 

assess the Nation’s water quality.

For additional information contact:

Chief, National Water-Quality Assessment Program

U.S. Geological Survey

413 National Center

Reston, VA 20192

Or access the NAWQA public website at http://water.usgs.gov/nawqa/

References Cited

Bricker, S.P., Clement, C.G., Pirhalla, D.E., Orlando, S.P., and Farrow, D.R.G., 1999, 

National estuarine eutrophication assessment—Effects of nutrient enrichment in the 

Nation’s estuaries: Silver Spring, Md., National Oceanic Atmospheric Administration, National Ocean Service, Special Projects Office and the National Center for 

Coastal Ocean Science, 71 p.

Carlisle, D.M., Wolock, D.M., and Meador, M.R., 2010, Alteration of streamflow magnitudes and potential ecological consequences—A multiregional assessment: Frontiers in Ecology and the Environment, v. 9, no. 5, p. 264–270, doi:10.1890/100053, 

accessed January 9, 2012, at http://www.esajournals.org/doi/abs/10.1890/100053.

DeSimone, L.A., Hamilton, P.A., and Gilliom, R.J., 2009, Quality of water from 

domestic wells in principal aquifers of the United States, 1991–2004—Overview 

of major findings: U.S. Geological Survey Circular 1332, 48 p. (Also available at 

http://pubs.usgs.gov/circ/circ1332/.)

Diaz, R.J., and Rosenberg, Rutger, 2008, Spreading dead zones and consequences for 

marine ecosystems: Science, v. 321, p. 926–928.

Dubrovsky, N.M., Burow, K.R., Clark, G.M., Gronberg, J.M., Hamilton P.A., Hitt, 

K.J., Mueller, D.K., Munn, M.D., Nolan, B.T., Puckett, L.J., Rupert, M.G., 

Short, T.M., Spahr, N.E., Sprague, L.A., and Wilber, W.G., 2010, The quality 

of our Nation’s waters—Nutrients in the Nation’s streams and groundwater, 

1992–2004: U.S. Geological Survey Circular 1350, 174 p. (Also available at 

http://pubs.usgs.gov/circ/1350/.)

Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., Martin, J.D., Nakagaki, 

Naomi, Nowell, L.H., Scott, J.C., Stackelberg, P.E., Thelin, G.P., and Wolock, 

D.M., 2006, The quality of our Nation’s waters—Pesticides in the Nation’s streams 

and ground water, 1992–2001: U.S. Geological Survey Circular 1291, 172 p. (Also 

available at http://pubs.usgs.gov/circ/2005/1291/.)

Hoos, A.B., and McMahon, Gerard, 2009, Spatial analysis of instream nitrogen 

loads and factors controlling nitrogen delivery to streams in the southeastern 

United States using spatially referenced regression on watershed attributes 

(SPARROW) and regional classification frameworks: Hydrologic Processes, 

v. 23, no. 16, p. 2275–2294, doi:10.1002/hyp.7323, accessed June 25, 2009, at 

http://dx.doi.org/10.1002/hyp.7323.

National Research Council, 2012, Preparing for the third decade of the National WaterQuality Assessment Program: Washington, D.C., National Academies Press, 185 p. 

(Also available at http://www.nap.edu/catalog.php?record_id=13464.)

Nolan, B.T., and Hitt, K.J., 2006, Vulnerability of shallow groundwater and drinkingwater wells to nitrate in the United States: Environmental Science and Technology, 

v. 40, p. 7834–7840, doi:10.1021/es060911u.

Schwarz, G.E., Hoos, A.B., Alexander, R.B., and Smith, R.A., 2006, The SPARROW 

surface water-quality model—Theory, application, and user documentation: 

U.S. Geological Survey Techniques and Methods, book 6, chap. B3, 248 p., available 

at http://pubs.usgs.gov/tm/tm6b3.

Stone, W.W. and Gilliom, R.J., 2009, Update of watershed regressions for pesticides 

(WARP) for predicting atrazine concentration in streams: U.S. Geological Survey 

Open-File Report 2009–1122, 22 p.

Toccalino, P.L., and Hopple, J.A., 2010, The quality of our Nation’s waters—Quality 

of water from public-supply wells in the United States, 1993–2007—Overview 

of major findings: U.S. Geological Survey Circular 1346, 58 p. (Also available at 

http://pubs.usgs.gov/circ/1346/.)

U.S. Environmental Protection Agency, 2006, Wadeable streams assessment—A collaborative survey of the Nation’s streams: U.S. Environmental Protection Agency, 

EPA 841–B–06–002, 2 p., accessed January 10, 2012, at http://www.epa.gov/owow/

streamsurvey/.

U.S. Geological Survey, 2012, The Midwest Stream Quality Assessment: U.S. Geological Survey Fact Sheet 2012–3124, 2 p. (Also available at http://pubs.usgs.gov/

fs/2012/3124.)

—By Gary L. Rowe Jr., Robert J. Gilliom, and Michael D. Woodside

Figure 3. In fiscal year 2013, NAWQA will be able to start every-year monitoring at only 100 of 313 surface-water sites recommended in the Science Plan. 

The program will also be able to sample only 79 of the 100 groundwater networks recommended for trends monitoring over the next decade.