DEQ’s Monitoring Efforts on the Big Hole River will Provide Insight into the Health of the Waterbody
HELENA—The Montana Department of Environmental Quality (DEQ) received reports of undesirable algae growth on the lower portion of the Big Hole River this summer. DEQ’s monitoring and assessment team conducted sampling to determine the density and extent of the algae growth.
“While we have limited resources, we work hard to be responsive to reports of algae blooms. We were able to sample the river for algae and macroinvertebrates within a week of receiving reports,” said Darrin Kron, DEQ’s water quality monitoring supervisor. “Water and biological samples provide data that helps assess the health of the river and determine if it’s meeting water quality standards.”
DEQ sampled for algae and macroinvertebrates in addition to conducting visual assessments at three locations on the Big Hole River from Melrose to Glen in July of 2023.
DEQ observed a moderate to high level of filamentous algae growth during the sampling event. This type of algae can be undesirable for recreationalists floating the river and may impact aquatic life by reducing oxygen levels in the water. Sample results for macroinvertebrate and nutrients are still being analyzed, while ash free dry weight showed elevated levels related to recreation. Ash free dry weight is an assessment tool used to determine undesirable algae levels. The data collected has not been reviewed for potential impacts to the fishery at this time.
Data from DEQ’s algae sampling events conducted in 2020 and 2023, along with nutrient data from volunteer monitoring conducted by the Big Hole River Foundation, may help DEQ determine if the river is meeting water quality standards for nutrients by comparing it to thresholds. All data collected will be evaluated for quality and sufficiency prior to completing a water quality assessment on the lower segment of the Big Hole River. An assessment reviews the health of a water body and determines if it needs to be listed on Montana’s impaired waters list.
Previous analysis conducted by DEQ in 2003 resulted in multiple impairment listings in the Big Hole River watershed. An impairment listing means the river is not meeting standards for certain pollutants and requires developing a Total Maximum Daily Load (TMDL). A TMDL determines how much of a pollutant a waterbody can take before it impacts water quality and identifies likely sources of pollution with recommendations to improve conditions. In 2009, two TMDL documents were released by DEQ and provided metals, sediment and water temperature targets for the Big Hole River.
“Due to previous work, this waterbody already has a framework on ways to improve water quality,” said Christina Staten, DEQ’s TMDL section supervisor. “Additional data from this year’s monitoring efforts will help further determine a path forward to improving the Big Hole River for recreationalists and landowners.”
Tags: Water quality and Press Release