Another Blow to the Big Hole River; Widespread Neon-Green Algal Bloom Emerges

This week, Upper Missouri Waterkeeper documented and notified the Montana Department of Environmental Quality (DEQ) of a miles-long neon-green noxious algal bloom emerging on the Big Hole River downstream of Divide. The new algal bloom adds to the suite of troubling conditions plaguing the river and basin this summer, including a major collapse in brown and rainbow trout populations, warm water temperatures prompting hoot owl restrictions, and low flows.

“A healthy river needs balanced physical, chemical, and biological processes, and all three on the Big Hole River are sadly degraded,” said Guy Alsentzer, Executive Director of Upper Missouri Waterkeeper. “In the face of climate change, trout population decline, and excessive nutrient pollution, we need to take decisive action with science-based solutions capable of restoring this world-class waterway.”

Benthic algal blooms such as the one on the Big Hole are typically the result of nutrient pollution combined with long summer days and hot temperatures. Algal blooms degrade recreational uses of rivers, and negatively affect fish populations and aquatic communities by decreasing oxygen concentrations in the river. 

Nutrient pollution in the Big Hole isn’t new. The Upper Big Hole and North Fork have had a pollution diet (total maximum daily load aka TMDL) to reduce existing sources of pollution in place since the EPA approved the plan in 2009. Unfortunately, the Montana Department of Environmental Quality (DEQ) has yet to review the Big Hole TMDLs and evaluate any progress made toward improving water quality standards or recommend management changes, a process that should occur every five years. 

The Big Hole River Foundation’s water quality monitoring data has consistently found unhealthy and elevated levels of nutrient pollution in the Big Hole. Prolonged and widespread algal blooms could cause serious harm to the health of the Big Hole River, impacting not only the fishery, but the local economy, jobs, and Montanans’ outdoor way of life. In a time of diverse river threats it’s critical our decisionmakers and agencies use all the tools on their tool-belts to protect river health and build resilience into the future.

For these very reasons, since July 2021, a broad coalition of outfitters, guides, businesses, NGOs, wild trout advocates, and concerned citizens have called on the Governor to form a multi-agency, Cold Water Fisheries Task Force to coordinate interagency response to new and emerging threats facing our waterways. 

Sadly, instead of prioritizing work on healthy rivers and fisheries, the state is actively rolling back science-based water quality standards and numeric nutrient criteria, and the 2023 Legislature initiated several rollbacks to longstanding pollution review and control criteria, including a prohibition on considering climate change impacts. Similarly, unrelenting new development pressure reliant on septic systems and exempt wells outside municipal boundaries continues apace, a trend that recent legislative bills only encourage, as opposed to mitigate. 

All the while Montana’s fisheries and river conditions continue to decline, a trend unlikely to improve without serious course-correction.