Blue-green algae outbreak occurs in Bailey Reservoir, possibly other locations in northeast Montana
By angelamontana

Posted: July 27, 2020

Last week, Montana Department of Environmental Quality (DEQ) notified Montana Fish, Wildlife & Parks of a blue-green bloom at Bailey Reservoir Fishing Access Site in Hill County. These algal blooms are not uncommon in waters across northeast Montana as we head into late summer and early fall. These outbreaks are known as Harmful Algal Blooms (HABs), as they sometimes pose health risks for people, pets, livestock, and wildlife.

HABs are caused by blue-green algae that are native to Montana’s freshwater lakes and reservoirs, according DEQ,. They are not Aquatic Invasive Species. Scientists believe the blooms are occurring at more locations, however, with increased frequency and longer duration than they have in the past. Causes may include warmer water temperatures, longer summer growing seasons and increased nitrogen and phosphorus runoff from a variety of human activities.

What does a HAB look like?

Blue-green algae blooms often look like pea soup, grass clippings, or green latex paint. The algae are usually suspended in the water column or aggregated into floating mats.

Not all varieties of blue-green algae are harmful, but some, under certain conditions, can produce dangerous poisons called cyanotoxins. The following are some recommendations and considerations concerning HABs:

  • Do not drink, swallow, or swim in water that shows signs of a HAB and be sure to keep kids and pets or livestock away from the water.
  • 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 and kidney damage.
  • It is not clear if consuming fish caught during Harmful algal blooms poses a health risk to humans. There have been no reports of people becoming sick from eating fish caught during a bloom, however there has been no definitive research assessing the risk to human health.
  • If you suspect a HAB-related illness in a person or animal, including livestock, call Poison Control immediately at 1-800-222-1222.

In past years, HABs have occurred at Bailey Reservoir (Hill Co.), Cow Creek Reservoir (Blaine County), Bearpaw Lake and Beaver Creek Reservoir (Hill County), Nelson Reservoir (Phillips Co.), and Medicine Lake (Sheridan Co.), along with other places around Montana When recreating at these reservoirs, please keep a lookout for HABs. When in doubt, stay out!

To learn more or to report a suspected HAB, please go to or call 1-888-849-2938. You may also report a suspected HAB by email to



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