Risks Associated with Harmful Cyanobacterial Blooms (HCB) Continue Despite End of Primary Contact Recreation Season

Water Quality Division
Published: Oct. 15, 2020

Although fewer people are recreating in Wyoming’s lakes and reservoirs this fall as water and air temperatures decrease, the Wyoming Department of Health, Wyoming Department of Environmental Quality, and Wyoming Livestock Board want to remind people, including hunters and fisherman, to continue to avoid and keep animals away from harmful cyanobacterial blooms that may be present. Although most blooms occur during the warmer summer and fall months and are expected to dissipate as temperatures decrease, some types of cyanobacteria are known to persist in freezing conditions and may continue to pose health risks to people and animals.

As shown on Wyoming’s HCB webmap, the Wyoming Department of Health issued recreational use advisories for twenty-one waterbodies during the 2020 season that ended on September 30th. The Wyoming Department of Health issued the advisories to inform the public that there may be health risks for people and animals that may come into contact with blooms present in these waterbodies. As outlined in Wyoming's HCB Action Plan, advisories remain in place until a bloom has fully dissipated and cyanotoxin concentrations fall below recreational use thresholds, or the primary contact recreation season ends on September 30th, whichever comes first. After September 30th, the Wyoming Department of Health will not issue new advisories, as the public health risks associated with HCBs are diminished due to the fact that cooler weather is likely to reduce the use of surface waters for swimming and similar water contact activities. The Wyoming Department of Environmental Quality will continue to receive reports and document new or potential HCBs until weather conditions deteriorate this fall and winter. Updated information will be included the HCB webmap. For more information on HCBs and recreational use advisories in Wyoming, visit WyoHCBs.org.

Potential health risks associated with blooms may still be present in waterbodies where HCBs have been documented. The Wyoming Department of Health and Wyoming Livestock Board continue to recommend the following:

  • Avoid contact with water in the vicinity of blooms, especially in areas where cyanobacteria are dense and form scums.
  • Do not ingest water from a bloom. Boiling, filtration and/or other treatments will not remove toxins.
  • Rinse fish with clean water and eat only the fillet portion.
  • Avoid water spray from a bloom.
  • Do not allow pets or livestock to drink water near a bloom, eat bloom material, or lick fur after contact.
  • If people, pets, or livestock come into contact with a bloom, rinse off with clean water as soon as possible and contact a doctor or veterinarian.

Questions about health effects and recreational use advisories can be directed to Dr. Karl Musgrave, State Environmental Health Epidemiologist / State Public Health Veterinarian, Wyoming Department of Health, at karl.musgrave@wyo.gov or (307) 777-5825.

Questions regarding HCB sampling and satellite imagery can be directed to Michael Thomas, Natural Resource Analyst, Wyoming Department of Environmental Quality, at michael.thomas@wyo.gov.

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