Harmful Cyanobacteria Blooms

Harmful cyanobacteria blooms (HCB's), commonly known as harmful algae blooms, are caused by a phylum of bacteria called cyanobacteria. Although many species of cyanobacteria naturally occur in Colorado waters, they may become a problem when they multiply rapidly, resulting in a "bloom", and that bloom is also producing toxins. Cyanobacterial blooms are often termed “potentially hazardous” because not all blooms produce toxins.

Cyanobacteria may resemble thick pea soup, spilled paint on the water's surface, and/or create a thick mat of highly colored foam along the shoreline. Bloom colors can be green, red, gold, or turquoise. Toxic cyanobacteria is typically not stringy like the harmless filamentous green algae so common in Grand County waters, nor is it mustard yellow in color, like pine pollen.

If you are concerned about cyanobacterial blooms in your reservoir, pond, or area water bodies, you can use the tools at the following resources to learn how to discriminate between potentially hazardous and safe conditions. 

If you do suspect a bloom:

  • Avoid skin contact with the water. Wash with clean water if contact does occur.
  • Don't drink the water.
  • Keep your pets and livestock away from the water.
  • Clean fish well with clean water and properly discard guts.

To report a suspected bloom, please complete this form. Please remember to include as much information related to the specific location as possible (GPS coordinates are preferred). 

For more information, please see the following resources:

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  1. Katherine Morris headshot

    Water Quality Manager

    Katherine Morris
    Ph: 970-725-3058

    Kayli Foulk headshot

    Water Quality Specialist

    Kayli Foulk
    Ph: 970-725-3750

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    Hot Sulphur Springs, CO 80451

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Harmful Cyanobacteria Bloom Examples

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