Full Breakdown
Montana DEQ Moves Toward Eutrophication Impairment Designation for Big Hole River
6/26/2026, 1:59:48 AM
Proposed Eutrophication Impairment for Big Hole River
The Montana Department of Environmental Quality (DEQ) announced at a Divide open-house meeting that it intends to list the Big Hole River as impaired for eutrophication. The draft, expected to be finalized no earlier than 2027, would formally recognize excessive algae linked to nitrogen and phosphorus loading and trigger Total Maximum Daily Loads (TMDLs) for those nutrients and for temperature.
Background: Algal Blooms and Water Use
The river, a prized freestone fishery supporting recreation and agriculture, has shown recurring summer algal blooms for at least six years. Conservation groups—including Upper Missouri Waterkeeper, Save Wild Trout and the former Big Hole River Foundation—have documented blooms, declining macroinvertebrate diversity, and a 40-year low in trout recruitment.
Stakeholders and Positions
DEQ water-quality chief Andy Ulven says the listing would “formalize that there is an issue on the mainstem” and provide a template for other medium-sized rivers. Darrin Kron, who oversees DEQ monitoring, notes that TMDLs would act as a “pollution diet” for the waterway. Conservation leader Guy Alsentzer (Upper Missouri Waterkeeper) calls the agency’s approach a “political hot potato” and urges numeric nutrient limits. The Republican-controlled Legislature passed House Bill 664, prohibiting numeric standards, a move contested by environmental groups.
Data on Flow and Nutrient Loading
Current flow is about 25 % of typical volume, while irrigation ditches operate at roughly 50 % capacity. The basin recorded one of its worst snowpacks, heightening drought risk. Trout recruitment has fallen to historic lows not seen in four decades.
Criticism, Legal Dispute, and Conflicting Standards
Upper Missouri Waterkeeper argues DEQ is avoiding acknowledgment of “unhealthy and unnatural nutrient loading” and has sued the state over House Bill 664, claiming the law violates the Clean Water Act. The lawsuit seeks a federal ruling, expected by 2027, that could require DEQ to adopt numeric standards instead of the narrative approach favored by the legislature.
Local Impacts
Rancher Erik Kalsta, a longtime member of the Big Hole Watershed Committee, worries that the designation’s messaging could worsen drought concerns, noting the river may run dry within weeks—a condition not seen since the late 1980s. Save Wild Trout executive Brian Wheeler says the river is flowing at about one-quarter of its usual volume and stresses that clean water remains essential.
Upcoming Actions
A federal district court hearing on House Bill 664 is scheduled for late 2024, with a decision anticipated in 2027. DEQ plans to draft TMDLs after the final impairment designation, potentially unlocking new restoration funding.
Verbatim Quotes
- “formalize that there is an issue on the mainstem” — Andy Ulven, DEQ Water-Quality Division Lead
- “political hot potato” — Guy Alsentzer, Upper Missouri Waterkeeper
- “I think the bigger worry for me is the messaging around this, especially on a bad drought year,” — Erik Kalsta, Rancher, Big Hole Watershed Committee
- “you can at least make sure what you have is clean.” — Brian Wheeler, Save Wild Trout Executive Director
