Health Unit warns of blue-green algae bloom

Blue-green Algae bloom confirmed at Dempseys Lake in Greater Madawaska

The Ministry of Environment, Conservation and Parks (MECP) has confirmed the presence of a blue-green algae bloom on and around the shore of Dempseys Lake.

Blue-green algae blooms are a natural seasonal phenomenon that may appear in lakes, rivers, and ponds. Dense blue-green algal blooms can make the water look like a bluish-green pea soup or a shiny paint slick. They have the potential to produce toxins that are harmful to people and animals. Direct contact with the toxin can cause skin irritation and, if ingested, it can result in vomiting, nausea, diarrhea, and abdominal pain.

RCDHU advises that people using Dempseys Lake and any body of water for recreational or drinking water purposes be on the lookout for algae blooms. If a confirmed or suspected bloom is visible, please take the following precautions:

  • Avoid direct contact with the bloom.
  • Avoid swimming in the vicinity of a bloom. Do not allow pets or livestock to swim in the water. Wait until at least 24 hours after the bloom has disappeared and the water is clear before resuming recreational use.
  • Avoid any use of the water for cooking or drinking. Do not let pets or livestock drink the water.
  • Be aware that boiling water will not remove toxins and may cause more toxin to be released into the water.
  • Toxins that may be released by blue-green algae are not removed by small-scale residential treatment systems, such as filtration, chlorination or ultraviolet light disinfection. Surface water is never a safe source of drinking water without effective treatment.
  • Residents should not rely on water jug filtration systems as they do not protect against the toxins.
  • Caution should be exercised when eating fish caught in water where blue-green algae blooms have occurred. Avoid eating the liver, kidneys and other organs of fish caught in the water.
  • On lakes and rivers where blue-green algae blooms are confirmed, people who use the surface water for their private drinking water supply should consider an alternate, protected source of water.
  • Report algae blooms to MECP spills action center at 1-866-663-8477.
    RCDHU will continue to work with MECP to monitor for blue-green algae in open bodies of water within Renfrew County and District.
  • For more information, please visit the Ministry of the Environment Conservation and Parks website at Blue-green algae | or the RCDHU website at

RCDHU Communications(2023,June22) Blue-Green Algae Bloom Found – Dempseys Lake, Greater Madawaska Twp. [media release]

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