National Water-Quality Assessment (NAWQA): 1991-2012
National Water-Quality Assessment Project (NAWQA)
A leading source of scientific data and knowledge on the quality of our Nation’s water resources
Water-Quality Topics
Read about USGS water-quality research on a range of topics, from pesticides to PAHs, from radionuclides to redox
In 1991, Congress established the National Water-Quality Assessment (NAWQA) Project to address where, when, why, and how the Nation's water quality has changed, or is likely to change in the future, in response to human activities and natural factors. This page discusses the first two decadal cycles of NAWQA research from 1991 through 2012.
► Read below about the first two decades of NAWQA research:
- First decade - Baseline survey of water-quality conditions in 51 river basins and aquifers
- Second decade - Synthesis reports on major water quality topics of national priority
► Explore current NAWQA research
The NAWQA Project was designed to run in decadal cycles. From 1991-2001, the first decade, the NAWQA Project conducted interdisciplinary assessments and established a baseline understanding of water-quality conditions in 51 of the Nation's river basins and aquifers, referred to as Study Units. Descriptions of water-quality conditions in streams and groundwater were developed in more than 1,500 reports. Non-technical Summary Reports, written primarily for those interested or involved in resource management, conservation, regulation, and policymaking and listed below, were completed for each of the Study Units. Non-technical national summary reports on pesticides, nutrients, trace elements, and volatile organic compounds (VOCs) also were completed, in which water-quality conditions were compared to national standards and guidelines related to drinking water, protection of aquatic life, and nutrient enrichment.
NAWQA activities during the second decade (2002-2012) focused in large part on national and regional assessments. These assessments built on continued monitoring and assessments in 42 of the 51 Study Units completed in the first decade (USGS Fact Sheet 071-01). During the second decade, there was an emphasis on synthesizing the results of the Study Unit investigations on major water-quality issues:
- Pesticides
- Nutrients
- Volatile Organic Compounds (VOCs) in Groundwater
- Ecological Health of Streams
- Trace Elements
New studies during the second decade focused on water-quality topics of national priority.
- Principal Aquifers
- Public-Supply Wells and Factors that Affect Their Vulnerability to Contamination
- Domestic Supply Wells
- Agriculture and Water Quality
- Nutrients and Stream Ecosystems
- Mercury in Streams
► Additional information on these and other water-quality topics
NAWQA Study Units
NAWQA Study Units covered a variety of important hydrologic and ecological resources; critical sources of contaminants, including agricultural, urban, and natural sources; and a high percentage of population served by municipal water supply and irrigated agriculture. Study Unit boundaries frequently croseds State boundaries and usually encompassed more than 10,000 square kilometers (about 3,900 square miles).
The Study-Unit design used a rotational sampling scheme; therefore, sampling intensity varied year to year at the different sites. In general, about one-third of the Study Units were intensively investigated at any given time for 3-4 years, followed by low-intensity monitoring. Trends in water-quality conditions were assessed about every 10 years.
Summary reports are listed below for the individual Study Units assessed during the first decade (1991-2001). Publications for principle aquifer assessments are listed at Groundwater Quality in Principal Aquifers of the Nation, 1991–2010.
Study Unit Summary Reports
(Number refers to the study units map, above)
1 - Acadian-Pontchartrain Drainages (LA, MS)
2 - Albemarle-Pamlico Drainage Basin (NC, VA)
3 - Allegheny and Monongahela River Basins (MD, NY, PA, WV)
4 - Apalachicola-Chattahoochee-Flint River Basin (AL, FL, GA)
5 - Central Arizona Basins (AZ)
6 - Central Columbia Plateau (ID, WA)
7 - Central Nebraska Basins (NE)
8 - Connecticut, Housatonic and Thames River Basins (CT, MA, NH, NY, RI, VT)
9 - Cook Inlet Basin (AK)
10 - Delaware River Basin (PA, NY, NJ)
11 - Delmarva Peninsula (DE, MD, VA)
12 - Eastern Iowa Basins (IA, MN)
13 - Georgia-Florida Coastal Plain (GA, FL)
14 - Great and Little Miami River Basins (OH, IN)
15 - Great Salt Lake Basins (UT, ID, WY)
16 - Hudson River Basin (NY, CT, MA, NJ, VT)
17 - Island of Oahu (HI)
18 - Kanawha-New River Basins (WV, VA, NC)
19 - Lake Erie-Lake Saint Clair Drainages (IN, MI, OH, PA, NY)
20 - Long Island-New Jersey Coastal Drainages (NJ, NY)
21 - Lower Illinois River Basin (IL)
22 - Lower Susquehanna River Basin (MD, PA)
23 - Lower Tennessee River Basin (TN, AL, GA)
24 - Las Vegas Valley Area and the Carson and Truckee River Basins (NV, CA)
25 - Mississippi Embayment (AR, KY, LA, MS, MO, TN)
26 - Mobile River Basin (MS, AL, GA)
27 - New England Coastal Basins (ME, MA, NH, RI)
28 - Northern Rockies Intermontane Basins (ID, MT, WA)
29 - Ozark Plateaus (AR, KS, MO, OK)
30 - Potomac River Basin (DC, MD, PA, VA, WV)
31 - Puget Sound Basin (WA)
32 - Red River of the North Basin (MN, ND, SD)
33 - Rio Grande Valley (CO, NM, TX)
34 - Sacramento River Basin (CA)
35 - San Joaquin-Tulare Basins (CA)
36 - Santa Ana Basin (CA)
37 - Santee River Basin and Coastal Drainages (SC, NC)
38 - South-Central Texas (TX)
39 - South Platte River Basin (CO, NE, WY)
40 - Southern Florida (FL)
41 - Trinity River Basin (TX)
42 - Upper Colorado River Basin (CO, UT)
43 - Upper Illinois River Basin (IL, WI, IN)
44 - Upper Mississippi River Basin (MN, WI)
45 - Upper Snake River Basin (ID, MT, NV, UT, WY)
46 - Upper Tennessee River Basin (GA, KY, NC, SC, TN, VA)
47 - Western Lake Michigan Drainages (MI, WI)
48 - White River Basin (IN)
49 - Willamette Basin (OR)
50 - Yakima River Basin (WA)
51 - Yellowstone River Basin (MT, WY, ND)
Access the links below to learn more about water-quality science.
National Water-Quality Assessment (NAWQA)
NAWQA has produced more than 1,500 reports that describe how water-quality and ecological conditions; whether conditions are changing over time; and how natural features and human activities affect these conditions.
The most recent publications and selected national-scale reports are listed here. See the USGS Publications Warehouse for all NAWQA publications.
► Pubs Warehouse FAQs
Water quality in the Willamette Basin, Oregon, 1991-95
Water quality in the White River basin, Indiana, 1992-96
Water quality in the Western Lake Michigan Drainages, Wisconsin and Michigan, 1992-95
Water quality in the upper Snake River basin, Idaho and Wyoming, 1992-95
Water quality in the central Columbia Plateau, Washington and Idaho, 1992-95
Water quality in the South Platte River basin, Colorado, Nebraska, and Wyoming, 1992-95
Water quality in the lower Susquehanna River basin, Pennsylvania and Maryland, 1992-95
Water quality in the Las Vegas Valley area and the Carson and Truckee River basins, Nevada and California, 1992-96
Water quality in the central Nebraska basins, Nebraska, 1992-95
Water quality in the San Joaquin-Tulare basins, California, 1992-95
Water quality in the Rio Grande Valley, Colorado, New Mexico, and Texas, 1992-95
Water quality in the Red River of the North Basin, Minnesota, North Dakota, and South Dakota, 1992-95
In 1991, Congress established the National Water-Quality Assessment (NAWQA) Project to address where, when, why, and how the Nation's water quality has changed, or is likely to change in the future, in response to human activities and natural factors. This page discusses the first two decadal cycles of NAWQA research from 1991 through 2012.
► Read below about the first two decades of NAWQA research:
- First decade - Baseline survey of water-quality conditions in 51 river basins and aquifers
- Second decade - Synthesis reports on major water quality topics of national priority
► Explore current NAWQA research
The NAWQA Project was designed to run in decadal cycles. From 1991-2001, the first decade, the NAWQA Project conducted interdisciplinary assessments and established a baseline understanding of water-quality conditions in 51 of the Nation's river basins and aquifers, referred to as Study Units. Descriptions of water-quality conditions in streams and groundwater were developed in more than 1,500 reports. Non-technical Summary Reports, written primarily for those interested or involved in resource management, conservation, regulation, and policymaking and listed below, were completed for each of the Study Units. Non-technical national summary reports on pesticides, nutrients, trace elements, and volatile organic compounds (VOCs) also were completed, in which water-quality conditions were compared to national standards and guidelines related to drinking water, protection of aquatic life, and nutrient enrichment.
NAWQA activities during the second decade (2002-2012) focused in large part on national and regional assessments. These assessments built on continued monitoring and assessments in 42 of the 51 Study Units completed in the first decade (USGS Fact Sheet 071-01). During the second decade, there was an emphasis on synthesizing the results of the Study Unit investigations on major water-quality issues:
- Pesticides
- Nutrients
- Volatile Organic Compounds (VOCs) in Groundwater
- Ecological Health of Streams
- Trace Elements
New studies during the second decade focused on water-quality topics of national priority.
- Principal Aquifers
- Public-Supply Wells and Factors that Affect Their Vulnerability to Contamination
- Domestic Supply Wells
- Agriculture and Water Quality
- Nutrients and Stream Ecosystems
- Mercury in Streams
► Additional information on these and other water-quality topics
NAWQA Study Units
NAWQA Study Units covered a variety of important hydrologic and ecological resources; critical sources of contaminants, including agricultural, urban, and natural sources; and a high percentage of population served by municipal water supply and irrigated agriculture. Study Unit boundaries frequently croseds State boundaries and usually encompassed more than 10,000 square kilometers (about 3,900 square miles).
The Study-Unit design used a rotational sampling scheme; therefore, sampling intensity varied year to year at the different sites. In general, about one-third of the Study Units were intensively investigated at any given time for 3-4 years, followed by low-intensity monitoring. Trends in water-quality conditions were assessed about every 10 years.
Summary reports are listed below for the individual Study Units assessed during the first decade (1991-2001). Publications for principle aquifer assessments are listed at Groundwater Quality in Principal Aquifers of the Nation, 1991–2010.
Study Unit Summary Reports
(Number refers to the study units map, above)
1 - Acadian-Pontchartrain Drainages (LA, MS)
2 - Albemarle-Pamlico Drainage Basin (NC, VA)
3 - Allegheny and Monongahela River Basins (MD, NY, PA, WV)
4 - Apalachicola-Chattahoochee-Flint River Basin (AL, FL, GA)
5 - Central Arizona Basins (AZ)
6 - Central Columbia Plateau (ID, WA)
7 - Central Nebraska Basins (NE)
8 - Connecticut, Housatonic and Thames River Basins (CT, MA, NH, NY, RI, VT)
9 - Cook Inlet Basin (AK)
10 - Delaware River Basin (PA, NY, NJ)
11 - Delmarva Peninsula (DE, MD, VA)
12 - Eastern Iowa Basins (IA, MN)
13 - Georgia-Florida Coastal Plain (GA, FL)
14 - Great and Little Miami River Basins (OH, IN)
15 - Great Salt Lake Basins (UT, ID, WY)
16 - Hudson River Basin (NY, CT, MA, NJ, VT)
17 - Island of Oahu (HI)
18 - Kanawha-New River Basins (WV, VA, NC)
19 - Lake Erie-Lake Saint Clair Drainages (IN, MI, OH, PA, NY)
20 - Long Island-New Jersey Coastal Drainages (NJ, NY)
21 - Lower Illinois River Basin (IL)
22 - Lower Susquehanna River Basin (MD, PA)
23 - Lower Tennessee River Basin (TN, AL, GA)
24 - Las Vegas Valley Area and the Carson and Truckee River Basins (NV, CA)
25 - Mississippi Embayment (AR, KY, LA, MS, MO, TN)
26 - Mobile River Basin (MS, AL, GA)
27 - New England Coastal Basins (ME, MA, NH, RI)
28 - Northern Rockies Intermontane Basins (ID, MT, WA)
29 - Ozark Plateaus (AR, KS, MO, OK)
30 - Potomac River Basin (DC, MD, PA, VA, WV)
31 - Puget Sound Basin (WA)
32 - Red River of the North Basin (MN, ND, SD)
33 - Rio Grande Valley (CO, NM, TX)
34 - Sacramento River Basin (CA)
35 - San Joaquin-Tulare Basins (CA)
36 - Santa Ana Basin (CA)
37 - Santee River Basin and Coastal Drainages (SC, NC)
38 - South-Central Texas (TX)
39 - South Platte River Basin (CO, NE, WY)
40 - Southern Florida (FL)
41 - Trinity River Basin (TX)
42 - Upper Colorado River Basin (CO, UT)
43 - Upper Illinois River Basin (IL, WI, IN)
44 - Upper Mississippi River Basin (MN, WI)
45 - Upper Snake River Basin (ID, MT, NV, UT, WY)
46 - Upper Tennessee River Basin (GA, KY, NC, SC, TN, VA)
47 - Western Lake Michigan Drainages (MI, WI)
48 - White River Basin (IN)
49 - Willamette Basin (OR)
50 - Yakima River Basin (WA)
51 - Yellowstone River Basin (MT, WY, ND)
Access the links below to learn more about water-quality science.
National Water-Quality Assessment (NAWQA)
NAWQA has produced more than 1,500 reports that describe how water-quality and ecological conditions; whether conditions are changing over time; and how natural features and human activities affect these conditions.
The most recent publications and selected national-scale reports are listed here. See the USGS Publications Warehouse for all NAWQA publications.
► Pubs Warehouse FAQs