Good News & Worse News For Mazinaw Lake Property Owners

Jeff Green | Nov 23, 2022

Based on a preliminary analysis of datasets from 2016 and 2021, members of the Mazinaw Lake Property Association became concerned about increased levels of phosphorus, mostly in the south basin of the large, deep lake. They were also concerned about increases in aquatic vegetation on the lake.

Mazinaw is the 7th deepest lake in Ontario, including the Great Lakes. It has an average depth of 41 metres and a maximum depth of 135 metres.

They asked the Mississippi Valley Conservation Authority (MVCA), which monitors the Mazinaw as part of its Lake Partner Program, to provide an analysis of the data, to help them decide if they need to take some action to mitigate against phosphorus levels having an impact on the functioning of the lakes ecosystem.

In a report, presented to the inaugural meeting of the 2022-2026 North Frontenac Council, Kelly Stiles, staff biologist with the MVCA, concluded that not only are phosphorus levels steady in the Mazinaw, but the lake is considered an oligotrophic, or low nutrient lake, with less than 10 parts per billion, on average, even in the highest nutrient south basin of the lake.

The concern about a high nutrient load in lakes is that they contribute to high vegetal growth rates and are associated with algal blooms, and other adverse outcomes.

But in addition to the news about phosphorus, Stiles report also said that aerial surveys show that the concern of the property owners association about increases in aquatic vegetation bear out, and that the main concern is with an increasing number of Eurasian milfoil.

“Photos of aquatic vegetation taken in September 2022 were used to confirm that Eurasian milfoil has become established in the lake and is the cause of the increased abundance of visible aquatic vegetation, in areas surveyed by the lake association. Eurasian Milfoil is a predominant invasive species in Ontario and is present in many Frontenac and Lanark county lakes.”

Stiles concluded her report by recommending that the property owners, and the municipality, continue to protect the shoreline and maintain the policy of requiring setbacks from the lake for all future development. She said the property owners and the township should also explore opportunities for shoreline enhancing. She also said that communicating the importance of “Clean Drain, Dry protocols for boaters as they move their boats from lake to lake is essential, as that is how the invasive Millfoil has been able to spread through Ontario lakes.