This summer’s warm weather has encouraged the growth of algae in Muskoka. Where there are plentiful nutrients, such as Phosphorus, in the water algae can grow rapidly producing “blooms”. Over 90% of algae is good for the environment and, while unsightly, harmless to humans. Blue green algae [actually a form of cyanobacteria] can be harmful to humans in sufficient concentrations.
In the below brochure from Muskoka Watershed Council shows an example of blue green algae. Harmful blooms typically look like pea soup or spilt paint with a bluish or greenish colour. If you suspect you have have a blue green algae bloom, please contact the Spills Action Center (1-800-268-6060 ). They will send an expert to visually identify the algae and, to take a sample for lab analysis if their expert confirms that it is blue green algae. Lab testing takes several days and will confirm if the concentration of harmful algae (called microcystins) exceeds the threshold harmful to humans.
In the interim, your site will be posted on the Simcoe Muskoka Health Unit website for water use restrictions. For example, Three Mile Lake, Clark Falls [Lake Rosseau] and Indianhead Harbour [Boyd Bay, Lake Muskoka] are currently posted. Click Here. According to SMHU there is no method to safely treat contaminated water. Not filtering, not boiling and not chlorinating. Please see their site for more detail.
Aside from expensive mass treatment of a waterbody with chemicals, there is no resolution of a confirmed bloom except to wait until it dissipates or repeat lab tests confirm microcystin levels are no longer harmful