Written by: A.J. Barney, Research Engineer for the Southwest Environmental Finance Center, Albuquerque, New Mexico

The EPA published final recommended ambient water quality criteria to address nutrient pollution in lakes and reservoirs under Section 304(a) of the Clean Water Act in August 2021. These recommendations address water quality standards for Total Nitrogen and Total Phosphorus to protect three designated areas: aquatic life, recreation, and drinking water sources. These recommendations include development tools based on stressor-response models that are designed to integrate state and national data to derive state-specific values that reflect local conditions. The Ambient Water Quality Criteria provides explanations of these tools to improve the adoption and development of the Numeric Nutrient Criteria recommended by the EPA in 2000 and 2001 for lake and reservoirs. If you are a regulator, or community member who may be impacted by these new criteria, the following information is presented to summarize and inform you about the Ambient Water Quality Criteria and what they mean for you.

Nutrient Pollution

Nutrient pollution occurs in natural waters when too many nutrients, mainly nitrogen and phosphorus, are introduced into those bodies of water. Agricultural discharge and the incomplete treatment of wastewater are the most common causes of nutrient pollution in natural waters. Excess nutrients in natural waters are a concern because they lead to degradation of water quality, feed harmful algal blooms, affect drinking water sources, increase public health risks, and contribute to costly impacts on drinking water treatment, recreation, tourism, and fisheries. Algal blooms and the resulting eutrophication are of notable concern, as they lead to oxygen depletion, which kills off wildlife present in the water, and can lead to discharges of harmful toxins. Nutrient pollution has even been cited as one of the three leading causes of impairment of the nation’s waters. 

Development of Ambient Water Quality Criteria

Nutrient pollution has previously been addressed through the integration of the EPA’s Numeric Nutrient Criteria into states and authorized Tribes’ water quality standards. These Numeric Nutrient Criteria set water type specific loading limits or ranges that states and authorized Tribes can use to develop monitoring standards for their natural waters, develop total maximum daily loads (TMDL), classify waters based on their achievement of water quality standards (WQS), and develop National Pollution Discharge Elimination Systems (NPDES) permits. These specific goals are in service of the broader goal of Water Quality Criteria, which is to protect aquatic life, recreational use of natural waters, and drinking water sources. The new Ambient Water Quality Criteria recommendations contain criteria development tools based on stressor-response models and can combine state and national data to derive state-specific values that reflect local conditions. These stressor-response models are data analysis models that use historical and new input data to model the impact of different pollutant loads on their receiving water. These results are used to help determine acceptable nutrient loadings into those same waters. These changes can further efforts to support state and authorized Tribes in developing and adopting Numeric Nutrient Criteria in their water quality standards. These models benefit from data sharing and allow states, territories, and authorized Tribes flexibility when developing Numeric Nutrient Criteria to apply to their water quality standards. 

Implementation of Ambient Water Quality Criteria

These types of tools and water quality criteria in general can feel daunting to stakeholders attempting to implement them, but the EPA provides a variety of online resources that can help regulators understand Ambient Water Quality Criteria and identify a starting point to begin using them. The first-place stakeholders should reference is the EPA’s Fact Sheet: Ambient Water Quality Criteria to Address Nutrient Pollution in Lakes and Reservoirs (pdf). This fact sheet provides a simple overview of the Ambient Water Quality Criteria. If you are looking to dive deeper into this information explore the EPA’s Final Frequently Asked Questions: Implementing the 2021 Recommended Clean Water Act Section 304(a) Ambient Water Quality Criteria to Address Nutrient Pollution in Lakes and Reservoirs (pdf). The EPA has designed Ambient Water Quality Criteria with the intention that water quality scientists do not need extensive modeling experience to use them and instead can use the EPA’s current resources and add to their databases to develop Numeric Nutrient Criteria. The Nutrient Scientific Technical Exchange Partnership and Support (N-STEPS) program was created by the EPA to provide technical assistance and technical guides towards Numeric Nutrient Criteria development and N-STEPS Online is their online resource library for technical support information. If state, territory, and tribal water quality agencies are still having trouble developing Numeric Nutrient Criteria the EPA provides the opportunity to request technical assistance through the Request for N-STEPS Support (pdf) form. If your agency is interested in implementing Ambient Water Quality Criteria these links are all a suitable place to start and the following websites also provide additional resources: 

Ambient Water Quality Criteria https://www.epa.gov/nutrient-policy-data/ambient-water-quality-criteria-address-nutrient-pollution-lakes-and-reservoirs

Numeric Nutrient Water Quality Criteria

How the New Ambient Water Quality Criteria May Affect Your Community

Ideally the implementation of the Ambient Water Quality Criteria would have overall positive impacts on receiving waters and nearby communities, but at this time, their impact is unclear. If the criteria are implemented as intended, community members can expect nearby receiving waters to function in a healthy and sustainable manner, with their intended uses to be fulfilled which may include for drinking purposes, recreation, to support aquatic life, or a combination of any of the three. Implementation of these criteria should provide community members with increased confidence about their nearby natural waters and the treatment of water that enters those waters. 

It is possible that the implementation of these criteria could result in an increase in the rigidity of current permit standards, which may require increased treatment of water being discharged into receiving waters. This can have a financial and logistical impact on community members. Utility user fees often increase when new infrastructure is required, and nearby community members are impacted by construction. 

While increased fees may seem unfavorable for community members, the benefits can outweigh the disadvantages if implemented correctly. It is up to those implementing new rules to research them properly to ensure that community members are engaged and informed properly to ensure sustainable water developments.