Grey Bruce Public Health has been notified that a blue-green algae bloom in a southern portion of Lake Eugenia in Grey Highlands has tested positive for the presence of naturally occurring toxins, known as microcystins, that can make people and pets sick.

The Ministry of the Environment, Conservation, and Parks collected samples from the bloom during a field visit on Aug. 15, 2024, and submitted them to a laboratory for testing.

Results of the tests, which have been shared with Public Health, show elevated concentrations of microcystins that are well in excess of federal recreational water quality guidelines and provincial drinking water standards.

As a result, Grey Bruce Public Health is advising people to not swim, play in, or use the water in the area of the algae bloom.

Blue-green algae, also known as cyanobacteria, are plant-like organisms that naturally occur in lakes, ponds, rivers, and streams, particularly in areas with warm, slow-moving, and shallow water. 

Blue-green algae can rapidly increase to form a large mass or scum, called a bloom. Dense blooms can make the water appear bluish-green, turquoise, or like green pea soup. Fresh blooms may smell like freshly mown grass, while older blooms can smell like rotting garbage.

Some varieties of blue-green algae can produce cyanotoxins, including a group of toxins called microcystins, that are harmful to human and animal health.

Human health effects from contact with cyanotoxins may include:

• Itchy, irritated eyes and skin from direct contact;
• Flu-like symptoms, such as headache, fever, diarrhea, abdominal pain, nausea and vomiting, if large quantities of toxins are swallowed.

When blue-green algae blooms are suspected or present, assume toxins are also present. It’s not possible to tell if toxins are present just by looking at a bloom.

If a bloom is present:

• Do not swim in the water.
• Do not let pets go into or drink the water.
• Do not let children play in or near the water.
• Be cautious about eating fish from the lake. Do not eat the liver, kidneys, or other organs of fish caught in the water body.
• Do not drink untreated water or use it for cooking. Boiling the water may increase toxins.

Although ingestion is the main concern, people or pets can also be exposed to the toxins in blue-green algae through inhalation or skin contact.

Suspected blue-green algal blooms can be reported by calling the Spills Action Centre at 1-866-663-8477.