Algal Blooms

Harmful Algal Blooms

Harmful Algal Blooms: Frequently Asked Questions

Algae warning issued for Loon Lake (Montcalm County) 7/9/2020


Dense populations of algae are called a bloom. Algal blooms can be found in lakes and can can contain flecks, foam or clumps. Some blooms are harmless, but some contain blooming toxic organisms, which can be harmful to humans, pets, and aquatic life. If you see algae, avoid direct contact with it and keep pets away as well.

Take the following actions if an algal bloom is present:

  • Do not drink untreated surface water, whether or not blooms are present. Remember, boiling the water will not remove the toxins.
  • Obey posted signs for public health advisories and/or beach closings.
  • Do not allow children or pets to play in or drink water where algae or scum is present.
  • Do not boat at high speeds, water-ski, or swim in areas of the lake where algal blooms are present. Avoid direct contact with the lake water or sprinklers.
  • Do not water lawns, gardens, or golf courses with water from impacted lakes or ponds because it aerosolizes the water.
  • Report unpleasant tastes or smells in your drinking water to the local water utility.
  • Individual property owners should not use algaecides because of the risk of releasing toxins directly into the water. Treatment requires a permit from the EGLE.
  • Do not have direct contact with mussels or other bivalves (i.e., zebra mussels) from impacted areas.
  • Limit or avoid eating fish from impacted areas. If fish are consumed, eat only the filets - remove guts and liver and rinse filets in clean drinking water. Always follow the Eat Safe Fish waterbody-specific guidelines or Statewide Safe Fish Guidelines, even if a waterbody does not look impacted, available at

People and pets can experience the following symptoms after contact with an algal bloom:

  • Skin contact may cause:
    • ¬†Rashes, hives, or skin blisters (especially on the lips and under swimsuits).
  • Breathing aerosolized (suspended water droplets) lake water mist from recreational activities and/or lawn watering can cause:
    • Runny eyes and noses
    • Sore throat
    • Asthma-like symptoms
    • Allergic reactions
  • Swallowing contaminated water can cause:
    • Severe diarrhea/vomiting and abdominal pain
    • Abnormal liver function
    • Kidney toxicity
    • Weakness, salivation, tingly fingers, numbness, dizziness, difficulties breathing, or death

If you think you have been exposed to an algal bloom, take the following precautions:

  • Remove people from the exposure and seek medical treatment if symptoms occur.
  • Thoroughly rinse off pets with clean, fresh water if they swam in an area with an algal bloom. If they lick their fur after leaving the water, they may ingest large amounts of the toxin.
  • Seek veterinary treatment as soon as possible if you think your pet might have been poisoned by toxic algae.


If you have questions or would like to report an algal bloom, contact Michigan Department of Environmental, Great Lakes and Energy (EGLE) at (include pictures if you can) or call 800-662-9278.