EPA has denied a petition from the Minnesota Center for Environmental Advocacy requesting the agency to develop national Nutrient Numeric Criteria (NNC) and Total Maximum Daily Loads (TMDLs) under the Clean Water Act for nitrogen (N) and phosphorus (P) in the Mississippi River Basin, the Gulf of Mexico and other related waterways where the standards do not currently exist.

The Mississippi River watershed drains all or part of the land area in 31 states between the Appalachian Mountains and the Rocky Mountains and carries that into the Gulf of Mexico.

EPA Deputy Assistant Administrator Michael Shapiro, in a letter to the environmental group, said that although EPA agrees that N and P pollution is a water quality problem, there already are many ways the agency is working with states and other government agencies like USDA’s Natural Resources Conservation Service to establish NNCs and TMDLs, and to improve water quality.