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Waters Assessed as Impaired due to Nutrient-Related Causes

Photos of assessed and impaired waters

About this indicator
Every two years states are required to submit Water Quality Assessment Reports under Sections 305(b) and 303(d) of the Clean Water Act describing the condition of waters in the state. These reports include water quality information on rivers, lakes, estuaries, and coastal waters, and an analysis of the extent to which waters are meeting water quality standards. Waters are assessed as impaired when an applicable water quality standard is not being attained. Impaired waters require a total maximum daily load (TMDL) or alternative restoration plan to reduce pollutant loadings and restore the waterbody. This indicator displays information about the extent of documented nutrient-related impairments of state surface waters (not including Great Lakes, coastal waters, or wetlands). This reflects states’ efforts to implement numeric and/or narrative criteria for nutrients by assessing waters for nutrient pollution and then listing waters as impaired to begin the restoration process. ‘Nutrient-related’ impairments include those from the following parent categories in EPA’s database, How is My Waterway?. Data provided in this indicator are for rivers/streams, lakes/reservoirs and bays/estuaries, and help demonstrate:

  • The extent to which a state is assessing its waters for nutrient-related parameters,
  • The extent of nitrogen and phosphorus pollution in the state, and
  • The extent to which the state is working towards restoring nutrient-impaired waters by developing TMDLs or alternative restoration plans.

To obtain more information on which waters have been listed by a state as impaired by nutrients and which of those waters have an associated TMDL, users can visit EPA’s How is My Waterway?.

In Integrated Water Quality Assessment Reports, each assessed waterbody or waterbody segment is listed in one of the five following categories (collectively these are the 305b data):

  • Category 1 – Attaining all designated uses
  • Category 2 – Attaining some designated uses, and insufficient or no data information to determine if remaining uses are attained
  • Category 3 – Insufficient or no data and information to determine if any use is attained
  • Category 4- Impaired or threatened for one or more uses but not needing a TMDL because –
    a) TMDL has been completed
    b) Expected to meet standards
    c) Not impaired by a pollutant
  • Category 5 – Impaired or threatened by pollutant(s) for one or more designated uses and requiring a TMDL. These are the waters entered onto a states’ 303(d) list.

In 305(b) Water Quality Assessment Reports, assessed waters are categorized according to the degree to which they support their designated uses:

  • Good water quality – fully supporting or fully supporting but threatened
  • Fair water quality – partially supporting (impaired)
  • Poor water quality – not supporting (impaired)

Data in this indicator on waters assessed as impaired due to nutrient-related causes include all Category 4 and 5 waters from Integrated Reports, and fair/partially supporting or poor/not supporting waters from 305(b) Reports.

References and links to other data sources

1. 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: US Geological Survey Circular 1350.

2. Shipp, A. and Cordy, G.E. 2002. The USGS role in TMDL assessments: US Geological Survey Fact Sheet 130-01.

3. US EPA. Overview of impaired waters and total maximum daily loads program.

4. US EPA. Ask Waters data query tool.

5. US EPA. WATERS Geospatial Data Downloads site.

6. US Geological Survey. National Water Quality Assessment Program (NAWQA): State Assessments of Beneficial Uses and Impaired Waters.

7. US EPA. Guidelines for Preparation of the 1996 State Water Quality Assessments (305(b) reports).

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