Since the end of July, the Simcoe Muskoka District Health Unit has issued six advisories for blue-green algae blooms. Two of those blooms affect lakes in Muskoka: Stewart Lake in the Township of Georgian Bay and Three Mile Lake in the Township of Muskoka Lakes. While the other four are on waterbodies in Simcoe County: Orr Lake, MacLean Lake, Midland Bay, and Hogg Bay.
Considering some blooms are toxic, the public health unit recommends that cottagers and locals on these waterbodies avoid swimming, boating, and playing watersports near the algae blooms. Residents who draw water from the lake should also avoid using it for drinking or food preparation, even with a filter.
“Some treatment systems may not remove the toxins from the water,” says Jenee Wallace, a safe water coordinator for the Simcoe Muskoka District Health Unit. And boiling the water won’t help either as heating it up could increase the number of toxins in the water.
Blue-green algae, also known as cyanobacteria, is naturally occurring in freshwater. Typically, the bacteria’s concentration is so small that it has no impact on the lake. But Wallace says blue-green algae can grow rapidly into dense blooms under certain circumstances.
“It can rapidly increase when the water is warm, slow moving, and when there’s a lot of sun, as well as a lot of nutrients, such as nitrogen and phosphorus,” she says.
These nutrients leach into the lake from people’s properties. Especially from fertilizers, cleaning products, and detergents. With enough nutrients, the blue-green algae can form a dense bloom, appearing as floating scum on the surface of the water. The bloom’s colour ranges from light green to turquoise.
Wallace stresses that not all blooms are toxic, but you can’t tell by looking at them. If you notice a bloom on your lake, you should contact the Ministry of Environment through its online reporting system. The ministry, in conjunction with the local public health unit, will test the bloom to see whether it’s toxic.
If you were to accidentally consume the water, it could lead to irritation of the skin, eyes, nose, throat, or lungs, stomach pain, headaches, diarrhea, vomiting, and in severe cases, liver damage. Head to a hospital if you’re experiencing these symptoms. The blooms are also toxic to pets. If your dog has been swimming close to a bloom, hose them off with clean water. If they start vomiting, head to a vet.
A bloom can also impact the health of your lake’s ecosystem. By blocking sunlight, the bloom prevents aquatic plants from growing, depriving fish and other species of necessary nutrients.
Once a bloom has appeared on your lake, it can be difficult to get rid of until the weather turns cold. Instead, Wallace suggests taking preventative measures to ensure blooms don’t form. This includes avoiding fertilizers, only using phosphate-free detergents and cleaning products, maintaining a natural shoreline to reduce run-off, and keeping your septic system in good condition so that it doesn’t seep into the lake.
These preventative steps could prove essential moving into the future as blue-green algae blooms are increasing. “Climate change definitely can impact the occurrence of blue-green algae blooms,” Wallace says. “Warmer days and increased warmer temperatures in the outdoor environment can result in more blooms in our water bodies.”