When is it safe to go back in the water?

This summer there have been a number of blue-green algae blooms reported in area lakes, resulting in warnings from the Simcoe Muskoka District Health Unit and the North Bay Parry Sound Health Unit.

Some confusion results when whole lakes are named in the warning, but the bloom is localized to a particular area. According to the Safe Water Manager for the SMDHU, Christina Weider, this is because conditions can quickly move the algae to other areas.

“Wind and wave direction can move the bloom,” she explains. “So that is why we issue the caution to the whole … lake for cottagers and residents to look out for these blooms.”

She says generally once the bloom disappears, and test results return things can get back to normal.

“Once the bloom dissipates and there are no toxins … we will lift the advisory,” says Weider.

Weider confirms that the issue of blooms is seasonal, dependent on a food source such as nitrogen and phosphorous and also warm water temperatures.

“So once the lakes start cooling off you start getting those less favourable conditions for the blooms to be growing,” Weider says.

The type of lake you are on goes a long way to predicting whether it will be susceptible to an outbreak.

“Where we have shallow lakes or slow-moving lakes it has helped for these blooms to appear,” she confirms.

Colder, deeper lakes are less likely to experience a bloom due to lake turnover, where warm top layers get heavier and fall, constantly being replaced by the cooler layer of water below.


with files from James Bowler