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Cyanobacteria Bloom

       October 24,2022

October 29,2022.

October 29,2022

A confirmed blue-green (Cyanobacteria) bloom has been found   along the mid-western shore of Leonard Lake. The Bloom was discovered by our water team member during routine shoreline sampling on October 24.  (see photos). Initial testing by our water team members confirmed elevated levels of the same species of blue-green algae (Dolichospermum) that has formed all blooms on the lake in the previous 5 years. This species is potentially toxic.   Officials from the Ministry of the Environment Conservation and Parks (MECP) responded promptly, and re-sampled the bloom. Their results confirmed the presence of a bloom and supported the initial findings of the water team.  While the bloom is not presently considered toxic, the MECP considers that toxins may be released over the next 2 weeks. Accordingly, the Simcoe Muskoka Health Unit has posted a Water Quality Advisory.  As of Saturday October 29, our water team reports that the bloom has become more intense, and has spread along the shoreline of 5 lots  of the mid-western bay.  Our team will keep   monitoring this bloom, and update MECP and LLSA on the status of the bloom.     

On three previous occasions this season, we have experienced similar events:  In mid-July, a scum (confirmed by our team as blue-green algae) occurred briefly (one day) at the same mid-western bay location where the August 24 Bloom occurred.  In   late August, repeated sampling at the boat launch found elevated blue green algae levels even though the water was clear.  When a scum (possible bloom) built up on August 25, MECP was contacted. Unfortunately, they responded after 4 days and did not find a bloom.  On October 6, another scum was reported along the south side of Outlet Bay. (see photo attached), and our testing found elevated levels of the same blue green species. Again, we contacted MECP, however, when they responded after 4 days to re-sample the bloom, it had disappeared.  Blooms can appear, and re-appear and move frequently during the season.


If you have any health questions about blue-green algae or about health precautions you can take, please visit the link Simcoe Muskoka District Health Unit or contact Health Connections directly at 1-877-721-7520.

In the interim, we suggest that you keep an eye on your shoreline - a brief daily check if you are at the lake - to see if there are any signs of algae accumulation, especially in the quiet water or protected areas. If you notice anything unusual, please contact   LLSA ( or a water team member (Bill Heatlie at 705-764-8720 or Ken Riley at 705-764-1695).

Public Notices of Blue-Green algae placed by Simcoe Muskoka District Health Unit October 28, 2022 and  resolved as of December 13, 2022. 

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