What is eutrophication?
“Eutrophication” is the fancy scientific word describing the over-saturation of a waterbody with nutrients, including nitrogen and phosphorus, resulting in unhealthy ecological conditions.
Excess nutrients can fuel algae and plant growth, which reduces oxygen and creates conditions harmful to fish and other aquatic life. Nutrients enter our waterways through a variety of ways. In rural areas, agricultural runoff from fields can wash fertilizers into the water, and in urbanized or developing areas with construction, nutrient sources can include treated wastewaters from septic systems and sewage treatment plants, and stormwater runoff that carries pollutants such as lawn fertilizers.
What is Montana DEQ proposing?
Montana DEQ is proposing a new method for determining whether nutrient pollution is impairing Montana’s wadeable streams and medium-sized rivers. The method would be used to determine whether a waterbody is meeting Montana’s water quality standards and supporting its designated uses (such as aquatic life and recreation), or whether it is impaired by nutrient pollution and requires a “pollution diet” or total maximum daily load (TMDL) to reduce pollution.
What are the main concerns with Montana’s proposed eutrophication assessment methods?
- It reacts to pollution instead of preventing it – This method is purely reactionary and provides no mechanism for preventing degradation, despite the law requiring a precautionary approach.
- The pollution thresholds are too high – The proposed limits for nutrients, dissolved oxygen, algae, and macroinvertebrates are too high to reliably protect rivers and sensitive species from nutrient pollution. The only streams and rivers that may be identified as impaired are those that show consistent signs of severe nutrient pollution.
- It does not require adequate monitoring – The Method allows inadequate sampling (such as assessing nitrogen and phosphorus with as few as 3 samples over 2 years, or not requiring sampling for nutrients at all), which will allow harm from nutrient pollution to go undetected for years.
- There is a high chance of failing to identify nutrient impairment – When impairment goes undetected, nutrient pollution will continue to contribute to ongoing and worsening degradation. Where impairment is detected, any response will be slow and inconsistent.
- It fails to protect downstream uses – The method fails to account for communities, businesses, and other downstream uses that depend on clean water and healthy rivers.
What will be the result of this proposed method?
More nutrient pollution will go undetected. Montana DEQ is essentially setting the bar for identifying eutrophication and harmful pollution so high that the majority of polluted waters will fail to receive the help they need. Because this method is so reactionary, and ‘triggers’ for action linked to dire conditions only, when a waterbody is finally recognized as impaired, it will already be suffering from severe pollution.
Montana’s Constitution requires that the State act in a preventative and anticipatory manner, not waiting until problems are severe, or beyond repair. Yet, DEQ is moving in the opposite direction and changing the way we manage pollution by making it more difficult to identify and address pollution. The agency is effectively turning a blind eye to negative ecological trends, which results in a statistical sleight-of-hand where, on paper, it will appear there aren’t many problems in our rivers despite the near-certainty that many river stretches and sensitive wildlife will in-fact be harmed before any action is required.
What happens when a river or stream is classified as “impaired”?
When DEQ determines a waterbody is impaired, it is added to the state’s list of impaired waters in the Water Quality Integrated Report. This is a requirement of the federal Clean Water Act, and incorporated into the Montana Water Quality Act under state law.
Identification of an “impaired” waterbody triggers a corresponding duty to develop a Total Maximum Daily Load (TMDL), or a “pollution diet,” which quantifies how much of a pollutant a waterbody can receive while still meeting water quality standards. The TMDL is used to ratchet down pollution sources and restore the health of the waterway.
Identifying pollution is the first step toward addressing it, and unfortunately, the new proposed Eutrophication Method makes it so difficult to identify a waterbody as impaired by nutrient pollution that most nutrients impairments will go unnoticed for years and pollution problems will worsen.
What happened to Montana’s numeric nutrient criteria and how does this relate to the legislative rollback?
In Spring 2025, the Montana Legislature passed and Governor Gianforte signed HB 664, a piece of legislation that rolls back numeric nutrient water quality standards for all water pollution control and water restoration purposes across the State.
Waterkeeper is actively litigating this unlawful rollback in federal court. Read more here.
This draft Eutrophication Method will serve as one of DEQ’s narrative nutrient regulatory tools following the elimination of numeric nutrient water quality standards.
What can you do to help?
Montana DEQ is accepting public comments on the proposed rule revisions now through September 11. Use your voice to speak up for the importance of protective, science-based eutrophication assessment methods – you can submit comments to DEQ here.