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State Progress Toward Developing Numeric Nutrient Water Quality Criteria for Nitrogen and Phosphorus

Numeric nutrient criteria are a critical tool for protecting and restoring a waterbody's designated uses related to nitrogen and phosphorus pollution. These criteria enable effective monitoring of a waterbody for attaining its designated uses; facilitate formulation of NPDES discharge permits; and simplify development of total maximum daily loads (TMDLs) for restoring waters not attaining their designated uses (i.e., impaired waters).

The interactive maps and tables below describe progress states are making towards the development of numeric nutrient criteria and the criteria they've developed.  Details about specific criteria in effect for Clean Water Act Purposes can be found at the following web page:

States and territories are also conducting additional activities to control nutrient pollution including watershed prioritization, setting goals to reduce nutrient loads, and other work.  However, this particular work is not reflected on this webpage.  More information about additional state efforts to reduce nutrient pollution can be found in the Nutrient Reduction Progress Tracker (PDF) (31 pp, 1 MB)Exit.

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N/P Criteria Progress Map

The map below shows a national summary of current numeric total nitrogen (TN) and total phosphorus (TP) EPA-approved criteria and those anticipated in the near future based on state-provided information. The information presented in the map is also presented in the interactive Criteria Status & Progress table.

Click the year of interest to see the relevant development status of TN and TP criteria. To see a summary for a state, move your mouse cursor over the desired state.

 

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Chlorophyll Criteria Map

The map summarizes current numeric EPA-approved chlorophyll-a criteria. The information presented in the map is also presented in the interactive Criteria Status & Progress table.

While total nitrogen and total phosphorus criteria are preferable for directly determining TMDLs and NPDES permit discharge limits, chlorophyll-a criteria can be used to determine if waters are impaired due to nitrogen and phosphorus pollution. Chlorophyll-a is a response variable that measures biotic productivity and activity, thus reflecting the nutrient enrichment of the system. Chlorophyll-a concentrations are a direct response to causal variables - total nitrogen and total phosphorus. See Technical Support for Numeric Nutrient Criteria Development.

To see a summary for a particular state, move your mouse cursor over the desired state.

 

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Table - Criteria Status & Progress

The table below shows a national summary of current EPA-approved numeric total nitrogen and total phosphorus criteria adoptions and those anticipated in the near future based on state-provided information. It also shows the status for related EPA-approved criteria such as chlorophyll-a. The information presented below is also presented in the interactive N/P Criteria Progress and Chlorophyll Criteria maps.

Sort the table by clicking on any desired column. For example, you can sort by state, region, and the level of progress. You can also Change Displayed Table Columns. For an explanation of the table symbols, click Table Legend or "mouseover" one of a states level cells (e.g., "Level 5").

 

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