Potential algae bloom on Willow Creek Reservoir prompts closure


Granby, Colo., July 31, 2021 – A potential toxic blue-green algae bloom in Willow Creek Reservoir has prompted officials to close this reservoir to water contact activities.  Willow Creek Reservoir is west of Highway 34 between Granby and Grand Lake and is normally open to non-motorized recreation only.  Forest Service officials are working in close coordination with Grand County, Colorado Parks and Wildlife, Bureau of Reclamation, Northern Water, and others to ensure the appropriate steps are taken to keep the public safe and assess when the area can reopen.

The public can find a complete map of area closures on our website.  Visitors to the Sulphur Ranger District of the Arapaho National Forest are reminded to always check the latest status of areas they plan to recreate on our website.

Algae are an important part of aquatic food webs, but some types of blue-green algae can produce toxins that may cause negative health impacts for humans and pets at elevated concentrations. Currently there is no method to remove toxins from lakes.  The Colorado Department of Public Health and Environment (CDPHE) recommends the following:

  • Keep kids out
  • No pets in water
  • Do not drink water
  • Avoid contact with algae

CDPHE describes Blue-green algae (also known as cyanobacteria) as a photosynthetic bacterium that is common and natural to waters found in all states, including Colorado. When water temperatures are warmer (commonly 20-25°C or 68-77°F) and extra nutrients are present most commonly in sunny yet still waters, these algae can multiply to form algal blooms. Some of the algae can start producing toxic compounds called cyanotoxins.  Recreational exposure can occur through incidental ingestion of water containing toxins during activities such as swimming, wading, surfing, jet skiing, and waterskiing. Young children and dogs are at high risk because they are most likely to accidentally (or intentionally) drink the water. 

For more information, watch this video created by Colorado Parks and Wildlife explaining Blue-Green Algae or click here to visit the CDPHE webpage on Toxic Algae.


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