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Cyanobacteria Bloom Information for Water Operators

Cyanobacteria Blooms in Surface Water Sources

Cyanobacteria, also known as blue-green algae, are naturally occurring microscopic organisms that are present in nearly all aquatic ecosystems in Illinois. When conditions are favorable, cyanobacteria can reproduce rapidly, causing blooms that may be visible to the naked eye. Blooms may look like blue or green spilled paint, cyan-colored crusts, green globules, or thick green scums.

These blooms have the potential to produce non-toxic byproducts such as geosmin and methyl-isoborneol (MIB). Both geosmin and MIB cause taste and odor issues in drinking water, even at low concentrations. When geosmin or MIB are present in finished drinking water, the water may have an earthy/musty odor or flavor. Though geosmin and MIB are not toxic, the taste and odor issues they cause can be a source of concern for the public.

Cyanobacteria may also produce toxins, known as cyanotoxins, that are harmful to humans if consumed. Cyanotoxins can break through to finished drinking water if treatment at water treatment facilities is insufficient. Boiling water will not remove toxins or make the water safe for consumption. Prioritize preventing blooms and treating drinking water to remove cyanobacteria and toxins. 

Treatment Options for Cyanotoxins in Drinking Water

Visit U.S. EPA’s webpage: Summary of Cyanotoxins Treatment in Drinking Water, for a list of treatment processes used to remove cyanotoxins from drinking water.

Issuing Drinking Water Advisories

On rare occasions, treatment at the water treatment facility may be insufficient and cyanotoxins may break through to the finished drinking water at levels of concern. In such case, a “do not drink” advisory must be issued if levels exceed recommended drinking water values and a “do not use” advisory must be issued if levels exceed recommended recreational values. Illinois EPA will provide recommendations but cannot issue advisories. It is the responsibility of the water treatment facility or municipality to issue and lift advisories. 

Example Template:  Do Not Drink Advisory

DO NOT DRINK Water Advisory

Do not boil water. It will not make it safe to drink.

The [water utility name] advises customers:

  • Do not consume tap water.
  • Do not use tap water to water pets or livestock.
  • Do not use tap water to brush teeth.
  • Use bottled water until the advisory has been lifted.

For more information, go to [www.watersystemwebsite.org] or call [###-###-####].

Example Template:  Do Not Use Advisory

DO NOT USE Water Advisory

Do not boil water. It will not make it safe to use or drink.

The [water utility name] advises customers:

  • Avoid using tap water.
  • Do not boil the water, as it will not make it safe to drink or use.
  • Do not consume tap water.
  • Do not use water for watering pets or livestock.
  • Do not use water for washing, bathing, watering, or medical devices.
  • Only use bottled water until the advisory has been lifted.

For more information, go to [www.watersystemwebsite.org] or call [###-###-####].

Treatment Options for Cyanobacteria Blooms in Surface Water

Visit U.S. EPA’s webpage: Control Measures for Cyanobacterial HABs in Surface Water, for a list  of methods for treating cyanobacteria blooms in surface waters. Some treatments include aeration, algaecides, and coagulation. The Interstate Technology Regulatory Council also has a list of control measures at Strategies for Preventing and Managing Harmful Cyanobacterial Blooms (HCB-1).

Prevention of Cyanobacteria Blooms in Source Waters

  • Reduce the amount of nutrients entering a waterbody by: 
    • cleaning up after pets or urban livestock;
    • planting native plants in riparian areas near waterbodies;
    • carefully following all directions when applying chemicals to lawns; and
    • properly maintaining septic systems.
  • Increase water flow by:
    • adding an aerator; and/or
    • installing a mechanical circulator.
  • Implement a HAB response plan using the Source Water Assessment Program (SWAP) mapping tool to help protect public water supply sources from bloom events. For more information regarding the SWAP mapping tool, please contact the Illinois EPA Bureau of Water, Groundwater Section, at (217) 782-1020.
Resources for Water Operators

U.S. Environmental Protection Agency

Centers for Disease Control and Prevention

Interstate Technology Regulatory Council

Illinois Environmental Protection Agency

WaterOperator.org