State of the Gallatin
To the uninformed angler, leisurely casting dry flies to eagerly awaiting cutthroat, the Gallatin may seem like a healthy waterway.
Its blue-ribbon designation and nearly 3,000 trout per river mile suggest the Gallatin enjoys a high level of ecological integrity, and in some ways it does–but it is also under threat from many angles. Large-scale nusiance algae blooms which first occurred in 2018, followed by repeat large-scale blooms in 2020 and 2022, serve as a visual indicator of the rivers compromised health.
2024 Gallatin River Report
2024 Data Results for Nutrients and Algae
2024 AT A GLANCE
No nuisance algae bloom was observed on the mainstem Upper Gallatin River in 2024, but blooms were observed along the West Fork, Taylor Fork and Beaver Creek. In 2024, water quality monitoring was conducted by the Montana Department of Environmental Quality (DEQ) along the mainstem Gallatin, and on the nine tributaries shown on the map by the Gallatin River Task Force.
EXCESS NITROGEN AND PHOSPORUS
While essential for ecosystems, excess nitrogen and phosphorus can be harmful. The West Fork, Middle Fork, and South Fork are impaired by excess nitrogen.
WARM WATER TEMPERATURE
Warm summer water temperatures likely led to algae blooms on the West Fork, but none were observed on the mainstem Gallatin despite similar conditions.
LOW STREAMFLOW
Streamflow was below average most of summer and fall except for brief periods after August rain events. Low flow promotes algae growth by increasing sunlight on the streambed.
WHAT CAUSES ALGAE BLOOMS?
Algae support stream health, but excessive blooms degrade water quality, harm aquatic life, and deter recreation. In 2018, large blooms on the Gallatin spurred a partnership between the Gallatin River Task Force and DEQ to study their causes. Research elsewhere links blooms to one or more of the following:
Low streamflow
Less water in the stream will cause the water to heat up more quickly, and allow more sunlight to reach algae growing on the streambed.
Lower water temperatures
Warm water temperatures The type of algae seen on the Gallatin can grow in temperatures from 50-77°F, but really thrives between 56.3-63.5°F.
Excess nitrogen and phosphorus
These are important nutrients for aquatic life, but having too much allows for algae to grow more than what is desirable.
Sunshine
More sunshine facilitates more algae growth.
What Was Unique About 2024
Despite conditions favoring a large algae bloom, none occurred on the mainstem Gallatin in 2024. Low winter snow, a cold, snowy spring, and a hot July led to extended runoff and late-summer low streamflow. This underscores the complexity of algae growth and the need for continued data collection to understand algae bloom drivers in the Gallatin.
Algae present on the West Fork
What's Next?
The next year of intensive study will complement data from 2024, giving a better understanding of the system and guiding management to protect the river. This will help guide a path forward backed by sound science. Luckily, steps are already in motion to ensure the Gallatin River runs clean and cold for future generations.