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Impaired Waters and TMDLs

Impaired Waters and Nutrients

Addressing nutrient pollution in our nation’s waters is a top priority. While essential for a healthy aquatic ecosystem, too much nitrogen and/or phosphorus in a waterbody can have detrimental impacts to aquatic life and human health and recreation. Too much nitrogen or phosphorus in a waterbody results in: overgrowth of aquatic plants, increased harmful algal blooms, decreased light penetration and decreased levels of dissolved oxygen. Each of these conditions make it difficult for fish to live and people to swim.

Tackling excess nutrients in our waterways is especially challenging in the 303(d) program. This is because most states rely on narrative water quality standards from which to base impairment decisions. Lack of numeric criteria for nitrogen and phosphorus adopted into state water quality standards and/or the inability to readily apply a narrative standard can be a barrier to listing a waterbody or identifying nutrients as the cause of the impairment. Developing Total Maximum Daily Loads (TMDLs) for nutrients is also difficult because nitrogen and phosphorus can come from any number of sources, e.g., a significant amount of nitrogen can come from agricultural or atmospheric sources.

Nutrient Resources

Nutrient TMDL Examples

Nutrient TMDL Workshop

February 15-17, 2011
EPA Regions together with EPA HQ, teamed up to offer a training workshop on the current practices being used in the Clean Water Act Section 303(d) Program to address waters impaired by nutrients. Thousands of waterbodies in the U.S. are impaired by the nutrient pollutants, nitrogen and phosphorus, and numerous challenges are associated with developing effective TMDLs for such waters. The purpose of this training workshop was to bring together EPA and state staff involved in the Clean Water Act Section 303(d) Program to exchange information related to development of nutrient TMDLs. The three day workshop covered a broad range of topics including section 303(d) listing, TMDL development and TMDL implementation for nutrient-impaired waters.

Nutrient TMDL workshop agenda.

Meeting Summary of Nutrient TMDL Workshop, February 2011, New Orleans, LA