Blue-green algae and affected waterways

If you suspect a blue-green algae bloom, speak to a public health inspector in the Health Protection Division by contacting Public Health Sudbury & Districts.

The Ministry of the Environment, Conservation and Parks (MOECP) has confirmed that these waterways have blue-green algae. The MOECP collects and tests algae samples and reports the results to Public Health Sudbury & Districts.

Waterways confirmed to have blue-green algae in the Sudbury and district area


Affected waterwayAreaDate
Whitson LakeSudburyJune 29, 2023
Helen Bay, Lake HuronManitoulinJuly 7, 2023
Horwood LakeChapleauJuly 14, 2023
Bass LakeManitoulinJuly 21, 2023
Ramsey LakeSudburyAugust 21, 2023
Boulder LakeSudbury EastOctober 6, 2023

What are blue-green algae?

Blue-green algae, technically known as cyanobacteria, are microscopic organisms that are naturally present in lakes and streams. They are usually present in low numbers. Blue-green algae can rapidly increase in warm, shallow, undisturbed surface water that gets a lot of sun. When this happens, they can form blooms that discolour the water or produce floating rafts or scum on the surface of the water.

What are the potential health effects from drinking or coming in contact with blue-green algae?

Some blue-green algae produce toxins (Government of Ontario) can pose a health risk to people and animals when they are exposed to them in large amounts. Your health may be impacted when surface scum or water containing high levels of blue-green algal toxins are swallowed, come into contact with the skin, or when airborne drops containing toxins are inhaled while swimming, bathing or showering.

Consuming water

Ingestion of high levels of blue-green algal toxins has been associated with effects on the liver and nervous system in laboratory animals, pets, livestock and people. Livestock and pet deaths have occurred when animals consumed large amounts of algal scum.

Direct contact or breathing airborne droplets

Coming in contact with high levels of blue-green algal toxins while swimming or showering can irritate the skin, eyes, nose and throat and inflame the respiratory tract.

Recreational contact

Swimming in, and household contact, such as bathing or showering, with water not visibly affected by a blue-green algae bloom is not expected to cause health effects. Some individuals, however, can be especially sensitive to even low levels of algal toxins and might experience mild symptoms such as skin, eye, or throat irritation or allergic reactions.

How can I avoid exposure to blue-green algae?

Never drink untreated surface water, whether or not algae blooms are present. Untreated surface water may contain other bacteria, parasites, or viruses, as well as algal toxins that could cause illness if consumed.

During an algal bloom, people not on public water supplies should not drink surface water , even if it is treated. In-home treatments—such as boiling and disinfecting water with chlorine or UV and water filtration units—do not protect from blue-green algal toxins.

People, pets, and livestock should avoid contact with water that is discoloured or has scum on the surface. Colours can include shades of green, blue-green, yellow, brown or red. If contact does occur, wash with soap and water or rinse thoroughly with clean water to remove algae.

Stop using the water and seek medical attention if symptoms such as skin, eye, or throat irritation, allergic reactions or breathing difficulties occur while in contact with untreated surface water. Swimming, bathing, or showering with water not visibly affected by a blue-green algae bloom is not expected to cause health effects.

Do not eat the liver, kidneys and other organs of fish caught in the water body. Be cautious about eating fish caught in water where blue-green algae blooms occur.

What should I do if I suspect blue-green algae?

If you suspect a blue-green algae bloom, speak to a public health inspector at Public Health Sudbury & Districts by calling 705.522.9200, ext. 464 (toll-free at 1.866.522.9200).

This item was last modified on June 24, 2024