What’s the source of Lake Ontario’s neon-blue hue?

Neon blue

Last week Lake Ontario turned a vibrant blue, not from a tie-dye project gone horribly awry or an impending alien invasion, but from algae.

The burst of colour, which stretched across the whole lake save for the most western point, was visible from airplanes or abroad the International Space Station, where an astronaut captured the neon blue waters with a camera. It was not, however, detectable from ground or water level, where hordes of Canadians savoured the last few days of summer, unaware of the phenomenon they were basking in.

According to Michael Twiss, a professor at Clarkson University in New York state who studies the Great Lakes, the electric blue hue was an effect of the “whiting event.”

The colour developed after the lake’s warm temperature allowed the microorganisms to flourish and photosynthesize, causing the water’s pH to rise. The pH level caused the calcium and carbonate ions that are naturally in the water to form white blocks of calcite on the organism’s surface. The white blocks reflect blue and green light, causing the “whiting” effect. After the water cools, the colour fades.
Although the effect used to be common in Lake Ontario, it’s a rare occurrence these days.

But if you love lake swimming, there’s no need to worry. Despite its resemblance to the harmful blue-green algae that renders water unsafe for swimming, this type of algae is non-toxic. Now, swimmers only have to worry about lake monsters lurking in the water, not some measly microorganism.