Progress towards Adopting Total Nitrogen and Total Phosphorus Numeric Water Quality Standards

About this indicator
This indicator provides information about states’ progress towards developing and adopting state-wide numeric water quality criteria for total nitrogen and total phosphorus for the three main waterbody types (river/streams, lakes/reservoirs, and estuaries). To protect waters from impairment, states develop, propose, and adopt water quality standards, or pollutant limits. EPA considers state adoption of numeric water quality criteria for nitrogen and phosphorus, the causal parameters directly responsible for eutrophication in immediate and/or downstream waters, a priority for water quality protection. Adoption of numeric criteria for nitrogen and phosphorus will facilitate and expedite the protection of waters by assisting states in identifying and listing impaired waters, developing total maximum daily loads (TMDLs), and writing National Pollutant Discharge Elimination System (NPDES) permits for facilities discharging nitrogen and phosphorus. Numeric criteria for nitrogen and phosphorus can also further improve water quality by assisting in best management practice implementation for non-point sources to limit nitrogen and phosphorus runoff and infiltration.

The information provided in this indicator shows whether or not each state has completed or provided dates for completing the following five milestones towards adoption of state-wide numeric total nitrogen and/or total phosphorus criteria for each of the three main waterbody types (river/streams; lakes/reservoirs, excluding the Great Lakes; and estuaries, where applicable): Planning for Criteria Development, Collection of Information and Data, Analysis of Information and Data, Proposal of Criteria, and Adoption of Criteria (EPA-approved). For more information on states’ progress towards adopting numeric nutrient criteria, refer to EPA’s website on State Development of Numeric Criteria for Nitrogen and Phosphorus Pollution. Additionally, visit states’ websites to learn more about their progress towards developing and adopting numeric total nitrogen and total phosphorus criteria.

What to consider when using these data
Some states may have numeric criteria for specific nutrient-related response parameters such as chlorophyll a (algae), and some states have site-specific total phosphorus and total nitrogen criteria. However, neither would be reflected in this indicator, which reports progress on adoption of total nitrogen and total phosphorus criteria for all waters within the state. For more information on states’ progress towards adopting numeric nutrient criteria, refer to EPA’s website on State Development of Numeric Criteria for Nitrogen and Phosphorus Pollution. Additionally, visit states’ websites to learn more about their progress towards developing and adopting numeric total nitrogen and total phosphorus criteria.

EPA has also developed a Criteria Search Tool that allows users to find water quality criteria EPA has approved for use under the Clean Water Act, including nutrients.

Source of data

This information is submitted by states in support of the National Water Program, and maintained by EPA internally. For more information on EPA’s performance measures, refer to the EPA Office of Water’s National Water Program Guidance.

References and links to other data sources

1. U.S. EPA. State Development of Numeric Criteria for Nitrogen and Phosphorus Pollution.

2. U.S. Geological Survey. National Water Quality Assessment Program (NAWQA): Nutrients and Eutrophication.