Waterkeeper’s Science and Advocacy Lead DEQ to Long-Overdue Big Hole River Protections; Concerns About Pollutants Driving Algal Blooms Remain
At a Big Hole River Open House last night in Divide, the Montana Department of Environmental Quality (DEQ) shared that it has made a draft decision to list the Big Hole River as impaired due to excessive algae growth. The agency plans to submit a proposal to list the river as impaired by eutrophication and low dissolved oxygen as part of the 2027 Water Quality Integrated Report.
“We’re encouraged to see DEQ and the Gianforte administration finally taking a step in the right direction for the world-class Big Hole River and the people and businesses that rely on it. 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,” said Guy Alsentzer, Executive Director of Upper Missouri Waterkeeper. “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.”
Nutrient loading and dissolved oxygen concentrations are critical chemical parameters of river health with direct impacts on fisheries and aquatic life. Western Montana’s freestone streams are highly sensitive to excessive and unnatural nutrient pollution. Extreme amounts of nitrogen and phosphorus can severely harm aquatic ecosystems, leading to the loss of sensitive species such as salmonids and disrupting the larger food web. Nutrient loading also fuels algal blooms, which cause large swings in dissolved oxygen (DO) levels, adding further physiological stress to salmonids and, when DO levels become low enough, can result in mortality.
The decision comes in response to a petition filed in February 2025 by Upper Missouri Waterkeeper and the Big Hole River Foundation requesting a Category 5 impaired waterway designation of the Big Hole River under Section 303(d) of the federal Clean Water Act (CWA). Along with the petition, five years of water quality monitoring data indicating clear exceedances of nitrogen and phosphorus water quality standards were submitted to the agency.
In April 2025, DEQ denied the petition and requested additional information, such as photo or video evidence of algal blooms, or macroinvertebrate data, so the agency could make an impairment determination based on narrative criteria rather than numeric, despite EPA’s express disapproval of Montana’s rollback of numeric nutrient criteria in 2022.
Following the petition disapproval, Waterkeeper sent a response letter to DEQ urging the agency to reconsider its decision in light of clarity regarding the continued applicability of numeric nutrient criteria to impairment decisions, and encouraging DEQ to “do the right thing, use all available science to determine the Big Hole River impaired for nutrients, and commit to working with petitioners and other stakeholders in addressing the pollution sources undermining this world-class waterway and harming the diverse uses it supports.”
After DEQ failed to take action to address undisputed water quality pollution events on the Big Hole, in May 2025 Waterkeeper filed a complaint in the Montana First Judicial District Court against the Montana Department of Environmental Quality (DEQ) for failing to apply legally-binding water quality standards in its denial of the petition. In June 2025, the court dismissed Waterkeeper’s legal challenge based on the idea that Waterkeeper needed to first administratively appeal to the Board of Environmental Review. BER’s track-record, however, is that of delay and obfuscation, which would further support DEQ’s plain effort of delay despite clear science indicating river impairment and the legal obligation to act on it.
More recently DEQ published a draft combined Integrated Report for 2022-24. The Integrated Report is a federally-mandated biannual publication to the EPA of what rivers within the state are or are not attaining their designated use at law, including a list of proposed impairment determinations. Waterkeeper provided public comment and additional scientific evidence from the most recent field season to DEQ regarding the Big Hole and again called for an impairment determination. DEQ’s Spring 2026 final Combined Integrated Report for 2022-24, however, did not take into account all available data, including not using numeric nutrient and dissolved oxygen data collected under the agency’s own protocols. That 2022-24 Combined Report is now pending review and action from the EPA, with a deadline of July 10, 2026.
DEQ’s newly announced intention to list the Big Hole River as impaired after years of delay is positive news. However, DEQ is not planning on taking action until the submission of the next draft Water Quality Integrated Report in 2027, which based on the agency’s track record is likely to take several years before its binding, enforceable, or pass-through restoration funding is available to address impairments (DEQ just submitted the 2022-2024 Water Quality Integrated Report to DEQ on June 12, 2026).
An impairment designation for the Big Hole River, and the associated resources and funding, needs to be proportional to the problems on the ground. The Big Hole is critical to Southwest Montana’s outdoor economy, local businesses, and drinking water for the city of Butte, and further delays or inaction will only exacerbate conditions on the ground.