What We Do
Monitor
Water Monitoring on the Gallatin River
For more than 25 years, the Gallatin River Task Force has monitored water quality, streamflow, temperature, nutrients, and algae to better understand the health of the Gallatin River and its tributaries.
2025 Gallatin River Report
2025 Data Results for Nutrients and Algae
*Although the state of Montana no longer applies numeric nutrient water quality standards (MT WQS), the 2025 data was compared to the former numeric MT WQS.
2025 AT A GLANCE
In 2025, the Gallatin River Task Force collected data on 7 tributaries of the Gallatin, while the Montana Department of Environmental Quality (DEQ) collected data along the mainstem Gallatin River.
No nuisance algae bloom was observed on the mainstem Upper Gallatin River in 2025, but blooms were observed along the South Fork, Taylor Fork, and Beaver Creek. Algae levels in these tributaries exceeded state thresholds.
What Causes Algae Blooms?
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. Though, just because algae blooms are observed, doesn’t necessarily mean excess nutrients are present.
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 for most of the summer and fall except for brief periods after August rain events. Low flow promotes algae growth by increasing sunlight exposure on the streambed.
PREVENTING ALGAE BLOOMS
Whether it’s supporting restoration efforts, maintaining your septic system, planting native, or picking up dog poop, there are several ways individuals and groups in our community can help:
Support Restoration
Our projects on both the West Fork and mainstem of the Gallatin restore natural conditions that function to absorb excess nutrients that feed algae, trap nutrient binding sediment, and block sunlight by planting shadegiving vegetation.
Respect Your Septic
Poorly maintained septic systems can leach nutrients into our groundwater. Get your system inspected annually, perform regular maintenance, pump the tank when indicated—generally every three to five years—and replace old or failing systems. Learn more.
Ditch the Fertilizers
Avoid using fertilizers, which can runoff and cause excess nutrients to enter our waterways. Instead, plant native species that can thrive without it.
Volunteer & Advocate
Volunteer to monitor tributaries with us and sign up for our spring Runoff Cleanoff event (be sure to pick up and properly dispose of your pet waste all year long!). Support our advocacy work for improving wastewater treatment and federal river protections through a federal Wild & Scenic designation.
Algae present on the West Fork
What's Next?
The next year of continued monitoring will complement data from 2024 and 2025, giving a better understanding of the system and guiding management to protect the river. This will help develop a path forward that is backed by sound science and best practices.
View the full 2025 Water Quality Report
WHAT WAS UNIQUE ABOUT 2025?
Despite conditions favoring an algae bloom, none occurred on the mainstem Gallatin in 2025. Early snowmelt, a warm spring, and a hot July led to extended runoff and latesummer low streamflow. This underscores the complexity of algae growth and the need for continued data collection to understand algae bloom drivers on the Gallatin.
Monitoring Reports
Since 2000, the Task Force has gathered water data to evaluate the health of the Gallatin River.
We use this data to build a record of chemical and physical indicators of water health and to identify and assess wide-spread algae blooms which have occurred in 2018, 2020, and 2022. This data guides our advocacy work and on-the-ground restoration efforts. Read the most recent water report from 2025 to learn more.
The Water Reports provide a comprehensive analysis of Gallatin River watershed conditions, while the Report Cards offers a concise summary of key findings and trends.
The Voice of the Gallatin River
Water Monitoring News
