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Development of Nutrient Criteria for Water Quality

In 2001, the U.S. Environmental Protection Agency published water quality criteria for nutrients (nitrogen and phosphorus) as called for in section 304(a) of the Clean Water Act. These criteria were developed as a starting point for states, authorized tribes, interstate commissions, et al., to develop criteria that would be appropriate for their own jurisdictions. This approach was due to the recognition that the determination of suitable limits for nutrients for water bodies is a highly complicated issue. It is governed by wide variation in local ecological conditions, as well as the uses placed upon the waters. Too much nutrient loading to a water body can cause rapid growth of algal blooms, organic enrichment and depletion of dissolved oxygen. Too little may result in insufficient enrichment of the aquatic food chain, which would be detrimental to a healthy aquatic biological community.

Developing the nutrient criteria that will protect the waters of the state requires significant analysis of water quality data. It also requires input from citizens concerned with the impact of implementation of nutrient criteria. With this in mind, a plan for developing nutrient criteria in Missouri was developed in 2005 and updates to the progress are presented here.


The first numeric nutrient criteria (NNC) for lakes and reservoirs were adopted as part of the water quality standards rule in October 2009. The currently applicable water quality standards for all NNC in Missouri are located at 10 CSR 20-7.031(5)(N), on page 18 of the water quality standards rule. The department has drafted a policy for implementation of the rule.

As part of water quality standards revisions adopted by the state, the standards must receive U.S. EPA (EPA) review and approval to be Clean Water Act enforceable, as described at 40 CFR § 131.5. The 2009 submittal received partial approval by the EPA for its site-specific NNC, now described at 10 CSR 20-7.031(5)(N)1.C.(II) and Table N. In response to the disapproved portions of the 2009 submittal, the department submitted water quality standards for review to EPA on April 13, 2018 with ecoregional NNC, located at 10 CSR 20-7.031(5)(N)1.C.(I) and Tables L and M. On Dec. 14, 2018, EPA approved the ecoregional NNC resulting in the originally approved site-specific NNC and the new ecoregional NNC Clean Water Act enforceable.

Numeric Nutrient Criteria for Missouri Lakes Fact Sheet

Rivers and Streams

Stakeholders began meeting in 2009 for briefings on how criteria development for streams will proceed.  These meetings were suspended so a technical workgroup could take the time necessary to make recommendations for criteria that will be scientifically defendable and sufficiently protective of the state's streams and rivers.  Criteria will be based on a compilation of several lines of evidence, including a statistical review of available data, a USGS study of algae response to nutrients in the Ozarks, and analyses of macro-invertebrates and chlorophyll-a as response variables.  When all analyses are complete, stakeholder meetings will be reconvened for consideration of the recommendations.