June 19, 2020
Potentially harmful algal blooms including blue-green algae are a natural seasonal phenomenon that may appear in our lakes, rivers and ponds. Many of these blooms are relatively harmless; however, some species have the potential to produce toxins which may be harmful to people and animals. The presence of a harmful algal bloom and its toxins can only be confirmed through a laboratory test, so we recommend taking a cautious approach when you suspect a potentially harmful algal bloom. Toxins that can cause skin irritation, nausea and vomiting, and in higher concentrations, liver problems are released when the cells break down.
The Health Unit advises people using surface water for recreation and drinking, to become familiar with potentially harmful algae so they can make informed decisions on when to avoid contact with the water. Algae blooms do degrade with time; however, it is not possible to say whether the toxins have completely left the area. Once the toxin is released from the cell, where it goes depends on the local characteristics of water movement in the area. The toxin will eventually be diluted into the body of water as any other soluble compound.
Surface water is never a safe source of drinking water without effective treatment. The toxins released by harmful algae are not removed by commonly used treatment methods such as boiling, chlorination or ultraviolet light treatment. Surface water requires specialized treatment. Consult a water treatment specialist if your drinking water comes from the lake. You may want to choose another source of water for drinking.
Recreational Water Use
Avoid activities that increase your exposure to toxins in the water during an active algae bloom. When deciding whether to resume recreational use of the water after a harmful algae bloom (swimming and water sports) consider the following factors:
- Faster moving water will dilute and move the toxins out of an area more quickly, further decreasing the risk to health. Each property will have a different water flow pattern, so a local assessment is useful to further assess risk.
- Skin irritation is the first sign that the level of toxin is significant in the water, so if this occurs, it is important not to go in the water. A few more days will help to clear the water if it is moving well, unless another bloom has occurred.
- The water in lakes and rivers always has the potential to be infected with bacteria, viruses and other microbes that can affect health. So it is important not to swallow the water. Young children are more likely to swallow water so it is critical to observe them carefully when in the water.
- Be cautious about eating fish caught in water where a harmful algae bloom has occurred. Toxins are concentrated in the liver. So avoid consuming the liver, kidneys and other organs of fish caught in an area affected by potentially harmful algae.
Algae exist in nature; however, they rely on certain conditions to grow. While we cannot control many of these conditions, we can influence one of the factors that affect their growth that is the nutrients available to them. You can help reduce nutrient levels entering the lake by reducing the use of household fertilizers, agricultural runoff, and ensuring your septic system is in good working order.
Residents are encouraged to contact the Spills Action Center at 1-800-268-6060 to report any new potentially harmful algae blooms. If possible take pictures of an active bloom as this may help identify the type of algae. This way the location and number of blooms can be monitored.
For more information about harmful algal blooms including blue-green algae, visit our Recreational Water page or call 1-800-660-5853.
Susan Healey, Communications Co-ordinator, Leeds, Grenville and Lanark District Health Unit at [email protected] or call 613-802-0550.