FAQs: Gallatin River Middle Segment Impairment Designation

June 2022 Preliminary Determination of Impairment

What’s being proposed?

Based on a review of best available science from the past 10 years, the Montana Department of Environmental Quality (DEQ) has issued a preliminary determination that the middle segment Gallatin River is not adequately supporting its designated uses due to severe, recurrent algal blooms, and therefore this river segment requires a formal impairment designation on the state’s 303d List of polluted waterways.

Why did DEQ propose listing the Gallatin River as impaired for “algal blooms” as opposed to nutrient pollutants?

Chemical monitoring of nutrient concentrations in the Gallatin did not reflect consistent exceedances of numeric nutrient water quality standards, yet the Gallatin experienced widespread algal blooms over the past four years.  This scenario indicates the Gallatin mainstem is likely more sensitive to nutrient pollution contributions than previously estimated under the state’s ecoregional specific numeric nutrient criteria. This relative uncertainty likely influenced the DEQ’s preliminary identification of “algal blooms” as the cause of impairment. 

What is clear is that algal blooms simply do not occur without nutrient loading; put another way, but for the presence of excessive nutrients in a river, the river cannot experience severe algal blooms.  Because the science of eutrophication and causal relationship between nutrient pollution and algal blooms is well-established, we encourage citizens to support DEQ’s preliminary determination of impairment with the caveat that the agency should clearly recognize that the pollutants of concern primarily causing or contributing to the Gallatin’s algal blooms are the nutrients nitrogen and/or phosphorus.  We expect that DEQ would fully examine those causal elements and use best available science in developing the requisite future TMDLs for the Gallatin.

What’s happening in the middle segment Gallatin River?

The middle segment Gallatin River, which stretches from the Yellowstone National Park boundary downstream to the confluence with Spanish Creek, has experienced consecutive years of unnatural algal blooms from 2018 to 2022.

River surveys during the 2018 and 2020 summer seasons documented “nuisance level” algal blooms that covered the mainstem Gallatin’s river bottom bank to bank, and for several continuous river miles downstream.  These severe blooms were then, and remain, unprecedented and, due to their consistency, their severity, and the known harms such pollution events effect for local water quality, for recreation, and for aquatic life, a significant cause for concern about whether the river is reaching an ecological tipping point. 

The term ‘nuisance algal bloom’ means a legally cognizable level of undesirable bottom-attached algae that is detracting from the recreational and aesthetic values of the river, and also has the potential to negatively affect aquatic life by degrading river habitat conditions for macroinvertebrate and/or fisheries.

Why should we care about big algal blooms in the Gallatin River?

Widespread, unnatural algal blooms indicate an imbalance exists within a freshwater river system.  In Montana the science is well-established that our headwater freestone streams, like the Gallatin, do not in their natural condition experience severe nuisance algal blooms.  Rather, decades of scientific research indicates that widespread algal blooms are nearly always linked to, first, new nutrient loading, and second, other contributing elemental factors.

Recurrent nuisance algal blooms in the Gallatin mean that the river is reaching a tipping point where it cannot assimilate all the different types of pollution entering its system.  The Gallatin has historically been recognized for its keynote trout fisheries and its cool, clean flows; after all, it flows directly out of Yellowstone National Park – it doesn’t get any cleaner than that!  Algal blooms degrade local water quality by lowering dissolved oxygen, altering pH, reducing quality conditions for macroinvertebrate communities, and elevating water temperatures, all of which threaten sensitive salmonid species and other aquatic life.  Similarly, severe algal blooms degrade recreational opportunities, as it’s much harder and less pleasant to fish, swim, or boat in prolific neon-green aquatic vegetation.  Montanans have legally protected rights to clean rivers, healthy fisheries, and river-based recreation, but rights are only worthwhile if they’re enforced!

What causes algal blooms?

Algae are a natural part of all aquatic ecosystems, but prolific growth can cause a dense mass of algae – called a bloom – to form.  While blooms are waterbody specific, the most common factors for algal bloom formation are nutrients, temperature, light, and consistent conditions.

Nutrients, and in particular phosphorus and nitrogen, are essential to algae production.  The availability of these nutrients encourage the growth of algae in freshwater systems like the Gallatin.  Increased nutrient loading above natural background levels often leads to increased algae production, and increased risk of a bloom.  This process of nutrient enrichment is called eutrophication, which can be further stimulated by man-made influences such as: shoreline development, certain agricultural practices, wastewater and industrial effluent, or urban and stormwater runoff.

Does the state have legal authority to address severe algal blooms in the Gallatin River?


The Montana DEQ is the delegated agency with authority to implement water quality protection and pollution control mandates of the federal Clean Water Act.  Similarly, the DEQ also implements the Montana Water Quality Act, a state law that intends to protect Montana citizens’ constitutional rights to a “clean and healthful environment.” 

Both of these laws require the DEQ to (a) identify rivers that are failing to remain clean, (b) to formally determine the severity of decline of any impaired waterway, and (c) if a waterway is failing to attain its protected legal uses (such as aquatic life or recreational uses), the agency must formally designate the waterway as ‘impaired’ at law and create and implement a mandatory pollution clean-up plan.

Why was a legal petition filed requesting designation of the middle segment Gallatin as impaired?

Montana DEQ is legally required to publish a biannual (every two years) list of waterways in the state that are failing to attain their designated uses.  Due to the pandemic and resource constraints the DEQ was unable to fulfill its duty of publishing the scheduled 2022 Integrated Report of Impaired Waters, which would have traditionally entailed soliciting public comment on any waters that have recently become degraded, including best available science supporting those concerns.  

When the DEQ last performed an Integrated Report there had only been one severe nuisance algal bloom on the mainstem Gallatin River.  From a scientific perspective one year of algal blooms can be an anomaly; several years constitutes sufficient evidence to take action.  So, when DEQ was unable to perform its duty in early 2022 to assess waterway health, local, regional and statewide conservation organizations worked together in combining their knowledge and expertise about the Gallatin River and submitted a formal legal petition to the DEQ requesting it recognize the writing on the wall and take action to address the Gallatin’s emerging pollution events, before it’s too late to correct course.

If the Dept. of Environmental Quality finalizes its preliminary determination and approves an impairment listing for the Gallatin River middle segment, what’s next?

Under state and federal law the Montana DEQ must respond to a legal impairment petition, an action it took earlier in June 2022.  The agency response in this case agreed with petitioners, specifically noting that the Gallatin River mainstem has experienced recurrent nuisance algae blooms and that those pollution events have degraded the river’s ability to attain the protected designated uses for aquatic life and recreation.

On June 20, 2022 the DEQ formally published a notice opening a 60-day public comment period concerning its Notice of Intent to List the Gallatin River middle segment as an impaired waterway on the state’s 303d List of Impaired Waters.  The public now has until August 22, 2022 to provide comments to the Department, and a public hearing is scheduled in Big Sky for 6pm on July 14, 2022.

After the close of the public comment period the agency will consider public comment and make a decision of whether to finalize its preliminary determination (that the Gallatin is impaired).  If the DEQ finalizes its preliminary determination, the next step is for the river to be formally added to 2020 Integrated Report as a “supplement” and that decision to be sent to the Environmental Protection Agency for approval.  Upon EPA approval, the Gallatin would be formally listed as impaired at law and the state would have a duty to develop a TMDL to address the contributing pollution.

What’s a TMDL (AKA, a river pollution diet)?

TMDL is an acronym standing for “Total Maximum Daily Load,” a term of art under federal water pollution control law.  A TMDL is a planning tool that provides the calculation of the maximum amount of a particular pollutant that a waterbody can receive and still meet applicable river quality standards.  Water quality standards include a designated use (the desired condition of the water) and parameter-specific criteria to protect the use.  

As part of the TMDL development process a science-based investigation will occur determining the key causal pollutants causing or contributing to recurrent algal blooms.  Then, those pollutants will be scientifically evaluated in terms of their sources and relative contributions to the river.  Then, for all sources, the TMDL will set “pollution caps” that limit the amount of pollutants from sources.  Those pollution caps will be enforceable in pollution permit decisionmaking for man-made sources and, for other sources, a variety of tailored best-management strategies will be designed and implemented for pollution reduction. The TMDL will remain in place indefinitely, and its efficacy will be measured through iterative annual monitoring of river health until the river regains its feet and nuisance algal blooms no longer occur.

Why are TMDLs critical tools for protecting the Gallatin River from algal blooms?

TMDLs are a proven, science-based process for identifying harmful river trends and developing transparent river restoration processes that are enforceable at law.  TMDLs offer a non-partisan guarantee that once river degradation is formally recognized, mandatory pollution control duties kick in to ensure a science-based accountability process for restoring river health begins.

How will a Gallatin River impairment determination affect economic development?

A Gallatin River middle segment impairment designation is a benefit for everyone and anyone who cares about the river, the local economy, or clear business expectations.  The TMDL process is driven by a non-partisan, science-based investigation of the pollution sources giving rise to negative water quality conditions, and a science-based cap on pollutant loading from those sources as needed to restore the river to health.

Thus, a Gallatin River impairment determination provides clear expectations of what we, as a community at the local, county, and state level, need to do to protect the river from nuisance algal blooms becoming the rule, not the exception.  TMDLs will provide businesses with regulatory certainty necessary to planning, will protect existing important river-based business’ interests in restoring and using cool, clean flows, and will provide transparency and an enforceable guarantee to the public that a transparent accountability framework for restoring the Gallatin to health is underway. 

What can I do to help?

Send the DEQ a comment letter!  There are two key points to make. 

First, support the DEQ’s preliminary determination that the Gallatin middle segment is impaired due to recurrent nuisance algal blooms.

Second, tell DEQ it needs to adopt well-established expert science showing that nutrient pollution is the key cause-and-effect of the Gallatin’s recurrent algal blooms, and therefore its final determination should reflect “nutrients, nitrogen and/or phosphorus” as the “pollutants of concern.”

Lastly, attend the public hearing in Big Sky on July 14th, 2022 and make these points in public comment.