State of Montana Newsroom
Potential Harmful Algal Bloom Reported at Noxon Reservoir in Sanders County
HELENA— A potentially harmful algal bloom (HAB) has been reported at Noxon Reservoir near the mouth of the Vermillion River and Kirby Boat Ramp in Sanders County. The bloom was first reported on Sept. 6, 2021. Harmful algal blooms are a proliferation of an organism called cyanobacteria. Not all varieties of cyanobacteria are harmful, but some, under the right conditions, can produce dangerous cyanotoxins. Direct contact, ingestion, or inhalation of cyanotoxins may irritate the skin, eyes, nose, throat, and respiratory system, or cause nausea, vomiting, diarrhea, headache, or liver or kidney damage.
Sanders County Sanitarian, Shawn Sorenson, sent the Montana Department of Environmental Quality a water sample from near the Kirby Boat Ramp for cyanotoxin testing on Sept. 22, 2021, and the results were “non-detect” for two common cyanotoxins—microcystin and anatoxin. At the time, the bloom had seemingly dissipated. Since then, more reports of a HAB near the mouth of the Vermillion River have been reported and a second set of water quality testing is anticipated mid-October. Updated toxin results will be posted on the citizen report map at HAB.mt.gov
Harmful algal bloom conditions can change rapidly so it is important for water users to educate themselves on what to look for. Common characteristics of HABs include green, blue, or gold coloration and the appearance of grass clippings or paint spilled on the water’s surface. A bloom could be visible in the morning and not producing toxins, but then visibly absent in the evening and cyanotoxins could be present. Cyanotoxins from the algal bloom can only be confirmed with water quality testing so it is best to avoid contact with suspected HABs.
Harmful algal blooms are native organisms to Montana’s freshwater lakes, reservoirs, and rivers. Blooms typically occur during summer months, although later in the fall is also possible. Scientists believe HABs are occurring at more locations, with increased frequency and longer duration due to factors like warmer water temperatures, longer summer growing seasons, and increased nitrogen and phosphorus inputs.
Citizens can report HABs on the website. This helps the state and counties conduct testing and identify locations of HABs in Montana waterbodies. Think you see a bloom? Give it room, grab a photo and submit your report to HAB.mt.gov