DEQ: Big Hole River is impaired by algae, nutrients
Laura Lundquist
(Missoula Current) The state of Montana has finally recognized that algae is degrading the Big Hole River, but one watchdog wants the state to act quicker to fix the problem.
After three organizations have pushed the state for several years to recognize algae problems in the Big Hole River, the Montana Department of Environmental Quality announced Tuesday evening that its recent assessment confirmed that the river is impaired by excessive nutrients and low dissolved oxygen caused by over-abundant algae. The organizations include Upper Missouri Waterkeeper, Save Wild Trout and Big Hole River Foundations.
DEQ held an open house on Tuesday in Divide to share updates about water quality studies and conditions in the Big Hole River. After attending the open house, Upper Missouri Waterkeeper and Save Wild Trout said in separate posts that DEQ had made a draft decision to list the Big Hole River as impaired by algae growth.
“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, Upper Missouri Waterkeeper executive director, in a statement. “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.”
Nutrients - a term for nitrogen and phosphorus compounds - are found in human and animal waste and in fertilizers because they encourage crop growth. The problem is nutrients also encourage algae growth when they pollute lakes and streams in a process called eutrophication. As large mats of algae spread across stream bottoms, the algae consumes oxygen in the water, leaving little for fish and other aquatic organisms. The process is exacerbated when streams have low flows and high water temperatures due to drought and climate change.
In 2019, DEQ authorized Save Wild Trout to start monitoring the river for nutrients, algae and dissolved oxygen. A year later, DEQ started receiving reports of large algae blooms, according to a timeline DEQ created for the open house.
Sampling 13 sites along the length of the Big Hole River, Save Wild Trout technicians found filamentous algae at all sites, but seven sites regularly had excessive amounts of algae covering 30% or more of the stream bottom. Also, nutrient levels were high at some sites, particularly near Wisdom where nitrogen exceeded water quality thresholds 93% of the time.
The Big Hole River Foundation looked at the data and saw “chronic exceedances of water quality standards for nitrogen and phosphorus at some sampling sites,” according to its website. So the Foundation and the Upper Missouri Waterkeeper petitioned DEQ in February 2025 to list the river as impaired for nutrients. In April 2025, DEQ denied the petition, saying the Legislature prevented the department from using numeric nutrient standards. Instead, they were to use less-accurate narrative standards that are often based on visual cues.
Unsatisfied, the Upper Missouri Waterkeeper tried to sue DEQ in May 2025 for refusing to use numeric nutrient standards that the U.S. Environmental Protection Agency had approved in 2016. But the judge dismissed the case, saying the Waterkeeper needed to pursue an administrative remedy through the Board of Environmental Review before turning to the courts.
Even so, DEQ decided to reassess the nutrient data. The result: “DEQ determined eutrophication and dissolved oxygen are impacting aquatic life and recreational uses in the Big Hole River,” according to a poster presented at Tuesday's meeting.
DEQ spokesperson Madison McGeffers told the Current in an email that “DEQ’s intended action will be shared with the public in July. Assessment outcomes will be officially proposed in the next draft Water Quality Integrated Report, which will be shared for public comment before being submitted to the federal Environmental Protection Agency for approval.”
Those “assessment outcomes” will be part of the draft 2026 Water Quality Integrated Report, which DEQ will produce next year. A Water Quality Integrated Report is a federally-mandated biannual report to the EPA of which Montana rivers are or are not fulfilling their designated uses, including a list of proposed impaired streams. But the reports can take time to compile, as evidenced by the fact that DEQ has only recently submitted its 2022-2024 report, which the EPA is supposed to review by July 10.
DEQ reportedly won’t do anything about nutrients in the Big Hole River until the 2026 Integrated Report is submitted to the EPA. Alsentzer said that could take another few years, maybe not until 2029, if it follows the course of the 2022-2024 report. That means enforcement actions and restoration funding associated with an impairment listing could be delayed for years too. So he wants DEQ to list the river now. It should have been part of the 2022-2024 report, Alsentzer said.
“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,” Alsentzer said.
Contact reporter Laura Lundquist at lundquist@missoulacurrent.com.