DEQ proposes Big Hole River as ‘impaired’

The Montana Department of Environmental Quality has determined the Big Hole River is impaired, which follows significant legal pressure from advocacy organizations.

The river has seen warm water, large algae blooms and dead trout, worrying both environmental groups and the guides who make their livelihood taking visitors fishing on one of Montana’s most renowned rivers. 

DEQ said in a statement it has determined that an overabundance of nutrients, called “eutrophication,” and poor oxygen levels are “impacting aquatic life and recreational uses in the Big Hole River.”

The details of worsening conditions will be added to the state’s next Water Quality Integrated Report, which is a federally-mandated document, expected next year. 

That report will have a public comment process before it is submitted to the Environmental Protection Agency, which has to approve the impairment declaration. If the EPA approves the action, it would likely require additional action by state and federal agencies.

If the EPA gives its approval, state and federal authorities will determine the limit for pollutants.

Officials already have implemented 91 categories for pollutants in the Big Hole River watershed, DEQ said in a statement, and added they’ve spent $1.3 million on restoration projects to date.

The work, so far, has been mostly focused on fixing erosion and adding vegetation.

Work has been done in the area since the 1980s, DEQ added, saying it supported the work by local watershed groups.

“Additionally, projects that reduce water temperature continue in the watershed,” a DEQ spokesperson said in a statement. “These efforts also reduce nutrients and help slow algae growth.”

The Big Hole River watershed has been the source of a legal fight between DEQ and environmental legal groups, specifically Upper Missouri Waterkeeper and the Big Hole River Foundation.

In a statement, Waterkeeper executive director Guy Alsentzer said they supported the move, but it had come too slowly.

“This action is way overdue and certainly better late than never, but we are still concerned about the agency’s pattern and practice of all-too-familiar delay tactics based on politics, not science,” Alsentzer said. “Everyone, including DEQ, has known about the Big Hole’s declining water quality for nearly a decade. Time is not on our side and further delays before action is taken are unacceptable for Montanans, local businesses, and our wild trout. DEQ needs to get to work yesterday to address the root causes of algae growth—nutrient pollution. If the agency fails to do so, all water users will suffer.” 

Waterkeeper and the Big Hole River Foundation filed a petition earlier this year asking for the impairment designation. The group even challenged the lack of action in state court, which was eventually dismissed. 

The DEQ responded to concerns that it has responded to Big Hole River problems too slowly:

“The Big Hole River is already an impaired water for other pollution listings such as sediment, temperature, flow, metals, and fish habitat. … DEQ has been working closely with Save Wild Trout to collect and review the necessary data. The final data package was provided to DEQ January of 2026. DEQ’s intended action will be shared with the public in July.”

One of the complicating factors for both groups and state officials has been a switch from numerical to narrative standards. In 2025, Montana switched from using data and numbers to relying on a narrative which advocates say has made proving scientific problems emerging from the river much harder. 

“Narrative prohibitions against causing harm, without an implementing rulebook, remain vague, imprecise, and naturally lead to permit writers making subjective decisions without clear metrics,” a Waterkeeper FAQ webpage reads. “Likewise, narrative prohibitions often require harm to occur before action is triggered. Waiting for harm to occur before requiring better pollution treatment is both bad policy and bad economics.”

DEQ has said it’s a helpful switch.

“Narrative standards describe conditions to be avoided and allow DEQ to identify impairments and develop plans to improve water quality,” a DEQ release from 2025 states. “The new law provides regulatory predictability for permittees and ensures DEQ uses the best science available to protect water sources based on the agency’s understanding of local, site-specific conditions.”

When asked for comment the Governor’s Office directed questions regarding allegations of slow walking the impairment designation to DEQ.

Editor’s note: This article was updated to reflect Montana is already eligible for federal funding for the Big Hole River.