The U. S. Geological Survey National WaterQuality Assessment (NAWQA) Program recently 

released the last 15 of 51 reports on water quality in 

major river basins and aquifers across the Nation. 

NAWQA began assessing the quality of our streams, 

ground water, and aquatic ecosystems in 1991.

Collectively, the new reports characterize the 

general health of our ground- and surface-water 

resources, address current and emerging water 

issues and priorities, and describe trends in water 

quality—a wealth of information that contributes to 

practical and effective water-resource management. 

Selected fi ndings of regional and national interest are 

highlighted in a separate report, Water Quality in the 

Nation’s Streams and Aquifers—Overview of Selected 

Findings, 1991-2001.

NAWQA assessments indicate that the Nation’s 

waters generally are suitable for irrigation, drinkingwater supply, and other home and recreational uses. 

Major challenges that continue to affect streams and 

ground water in parts of every study unit include point 

and nonpoint sources of pesticides, nutrients, metals, 

gasoline-related compounds, and other contaminants.

These assessments use a nationally consistent 

design and methodology so that water-resource 

managers can compare water quality in their basins 

to other areas in the Nation. The assessments also 

delineate the effects of natural factors and human 

activities on water resources, such as effects 

associated with agriculture and urban development. 

Contaminant levels vary from season to season and 

among watersheds because of differences in land and 

chemical use, land-management practices, degree of 

watershed development, and natural features, such 

as soils, geology, hydrology, and climate. Using this 

information, decision makers can implement costeffective water-management strategies in specifi c 

geographic areas.

Selected highlights from NAWQA reports 

Changes in land management can improve streamwater quality. For example, best management practices 

that began in the 1990s in much of the Yakima River 

Basin, Washington (such as converting from rill, or 

“furrow,” irrigation to sprinkler and drip irrigation) 

have reduced runoff from farm fi elds, thus reducing suspended sediment, total phosphorus, dissolved 

nitrate, and organochlorine compounds (such as DDT) 

in streams. Concentrations of total DDT (DDT and 

its stable breakdown products) in largescale suckers, 

smallmouth bass, and carp from the lower Yakima River 

decreased by about half from the late 1980s to 1998.

Ground-water quality also responds to changes in 

land management, but usually more slowly than 

surface water. USGS ground-water age-dating techniques used on the Delmarva Peninsula (Delaware, 

Maryland, and Virginia) indicate that improvements in 

ground-water quality, including reduced concentrations 

of nitrate from agricultural fertilizers, can lag behind 

land-management changes by decades because of the 

slow rate of ground-water fl ow.

Urbanizing watersheds show positive and negative 

changes in water quality. NAWQA sampled sediment 

cores from 42 reservoirs and lakes in 20 metropolitan 

areas across the Nation from 1996 to 2001, including near Chicago, Los Angeles, Salt Lake City, and 

Newark. Data show decreasing concentrations of lead, 

PCBs, and DDT since their use was restricted in the 

1970s, whereas polycyclic aromatic hydrocarbons 

(PAHs) generally are increasing in urbanizing watersheds with increased motor vehicle traffi c.

Even low levels of urbanization can affect aquatic 

ecosystems, as shown by stream-ecology studies in the 

Anchorage, Birmingham, Boston, Chicago, DaytonCincinnati, Los Angeles, Philadelphia-Trenton, and 

Salt Lake City metropolitan areas. For example, aquatic 

insect communities are affected when watersheds reach 

about 5 percent impervious area in Anchorage (which 

correlates with a population density as low as 125 to 

250 people per square mile).

U.S. Department of the Interior

U.S. Geological Survey Printed on recycled paper

Fact Sheet 2004–3045

May 2004

New reports on our Nation’s water quality
The infl uence of natural features can be substantial. 

For example, mercury concentrations are affected by 

the amount of wetlands and the presence of sulfur, carbon, organic matter, and dissolved oxygen in the soils 

and water. Concentrations of total mercury were higher 

in sediment in urban watersheds in the Boston metropolitan area than in adjacent, more forested watersheds 

in Maine and New Hampshire; however, concentrations 

of total mercury in fi sh (most of which was the most 

toxic form, methylmercury) were higher in fi sh in the 

forested watersheds, in large part because of the larger 

amount of wetlands.

NAWQA analyses detect very low levels of pesticides and volatile organic compounds (VOCs). 

There was widespread detection of these compounds, 

albeit often at low concentrations, in river basins and 

aquifer systems across a wide range of landscapes and 

land uses. In the mostly agricultural Lower Tennessee 

River Basin, for example, 52 different pesticides were 

detected in streams and rivers, and VOCs were detected 

in about 67 percent of sampled springs and wells that 

tap underlying carbonate aquifers.

Streams and ground water in watersheds with signifi cant agriculture or urban development usually 

contain mixtures of VOCs, nutrients, pesticides, and 

their chemical breakdown products. In Oahu, for 

example, VOCs and pesticides were detected together 

in more than half of sampled public-supply wells, with 

one exception. Few contaminants were detected in 

Honolulu due to a century of urban planning and watershed protection that directs intensive chemical use and 

storage away from upland recharge areas of the city.

Some contaminants occur naturally, even in relatively pristine areas like the Yellowstone River Basin 

in Wyoming and Montana. Elevated concentrations of 

phosphorus in streams are derived from igneous and 

marine sedimentary rocks; elevated concentrations of 

arsenic most likely result from sedimentary rocks in 

contact with geothermal waters. 

Findings provide information for decisions at 

local, State, and national levels

The USGS provides . . . top quality data and accurate reporting 

that both the farming community and the environmental 

community can trust. NAWQA’s ability to look at water quality 

over the long term helps to evaluate the effectiveness of watermanagement decisions, conservation activities, and certain 

farming practices that are used to reduce sediment and runoff 

of agricultural nutrients and chemicals from fi elds. Jeff Loser, 

National Leader for Clean Water Programs, USDA Natural 

Resources Conservation Service

The combined surface- and ground-water quality and ecological 

assessments of the Flint River Basin by the Lower Tennessee 

River Basin NAWQA Program have heightened our awareness 

of how vulnerable our water resources are due to karst features 

of the watershed. These technical, interdisciplinary assessments 

of watershed conditions have helped focus our watershed 

restoration efforts within the Flint River Basin. Susan Weber, 

Flint River Conservation Association

Data from the NAWQA Program supplied critical information 

for Ohio EPA’s Total Maximum Daily Load (TMDL) effort in 

the Stillwater River Basin, and will continue to provide valuable 

data for future TMDLs in other sub-basins of the Great Miami 

River. Robert Miltner, Aquatic Ecologist, Ohio Environmental 

Protection Agency

The NAWQA Program has fi lled a tremendous void in the 

pesticide data that the State of Alabama must acquire in 

the development of the USEPA-mandated State Pesticide 

Management Plans. Tony Cofer, Program Director—Pesticide 

Division, Alabama Department of Agriculture and Industries

Alaska’s social and economic fabric is inextricably bound to 

the health of our salmon habitat and water quality. The NAWQA 

Program has played a critical role in helping policy makers, 

businesses and citizens better understand the complexities of our 

watersheds, and as a result, we now have better tools to manage 

our salmon and water resources for future generations. Bob 

Shavelson, Executive Director, Cook Inlet Keeper, Alaska

The NAWQA study has been very valuable to the U.S. 

Environmental Protection Agency’s New England regional 

water programs. The study has provided contaminated sediment 

data, which will be incorporated into our National and regional 

sediment inventories; has highlighted the importance of arsenic 

in drinking water wells in New England; and has established 

relationships between land use and environmental quality of 

rivers and streams, including fl ow, nutrient status, and biological 

communities. The data from, and the monitoring approaches of, 

the study will help the USEPA in its monitoring and regulatory 

roles. Matthew Liebman, Environmental Biologist, U.S. 

Environmental Protection Agency-New England

This fact sheet is based on Hamilton, P.A., Miller, T. L., and Myers, D.N., 

2004, Water quality in the Nation’s streams and aquifers—Overview of 

selected findings, 1991-2001: U.S. Geological Survey Circular 1265, 20 p.

The NAWQA Program has launched a second round of 

monitoring, research, and assessment in 42 of the 51 study 

units. The main goals are to determine trends at many of the 

sites, fill critical gaps in the characterization of water-quality 

conditions, and increase understanding of natural and human 

factors that affect water quality. 

For additional information, contact NAWQA Chief, 703-648-

5012 dnmyers@usgs.gov 

For NAWQA publications, maps, data, and descriptions of 

program activities, visit water.usgs.gov/nawqa