Cyanobacteria
Blue-green streaks or clusters may appear at different times during the summer season on Brome Lake. These formations are cyanobacteria, commonly known as “blue-green algae.” Their presence can vary depending on weather conditions and water quality.
Cyanobacteria are a natural part of aquatic ecosystems. They are among the oldest forms of life known on Earth. Their presence does not automatically indicate a problem. However, when they multiply rapidly and accumulate on the surface of the water, they form a bloom that may pose a health risk.
Why do they appear?
Certain conditions can promote the growth and accumulation of cyanobacteria, including:
- hot and sunny days;
- high water temperatures;
- calm weather and a lack of waves;
- the resuspension of sediments;
- an increased supply of nutrients, particularly phosphorus and nitrogen, from shorelines, watercourses and runoff.
Wind and waves can then push cyanobacteria toward the shore, where they accumulate in streaks or clumps. A bloom can be very localized and may not affect the entire lake.
How to recognize them?
Cyanobacteria can take on different appearances:
- small green flakes dispersed in the water;
- streaks or clumps on the surface;
- an appearance similar to broccoli soup;
- a layer resembling spilled paint.
Water blooms are often very localized. They may be visible in one area of the lake and absent elsewhere. A localized observation therefore does not mean that the entire lake is affected.
Some cyanobacteria can produce toxins known as cyanotoxins. These toxins are not always visible or detectable by smell and can cause skin irritation, digestive problems or other health issues in the event of contact with or ingestion of contaminated water.
When green flakes are dispersed and the water remains sufficiently clear, recreational activities can generally continue. However, if the water bloom is denser or takes the form of scum (broccoli soup or paint-like streaks), it is best to avoid swimming and activities that may result in contact with the water.
- Avoid direct contact with a water bloom;
- Do not drink lake water;
- Keep children and pets away from water blooms.
Because water blooms are often localized, you may engage in recreational activities as long as you maintain a distance of 3 metres from them.
If you think you have come into direct contact with cyanobacteria, rinse yourself with drinking water and promptly contact medical services if you develop symptoms.
How to help prevent their spread?
Reducing the amount of nutrients reaching the lake helps limit the growth of cyanobacteria. Residents can help by:
- maintaining a vegetated shoreline buffer;
- limiting shoreline erosion;
- reducing runoff into the lake and waterways;
- avoiding the use of fertilizers near the lake;
- ensuring that their septic system is properly functioning and watertight;
- limiting the resuspension of sediments by adapting boat speed and routes in shallow areas.
Have you spotted a possible water bloom? Send the Town a detailed description, the exact location and photographs at the following email address: environnement@lacbrome.ca.
To learn more about the different categories of water blooms, click here (in French only).