For the first time in 17 years, Lake Superior is almost completely covered in ice — a phenomenon that could lead to a cooler summer and spring flooding in Thunder Bay, according to a Great Lakes researcher. 

Thanks to extremely cold winter temperatures, almost 96 per cent of the largest Great Lake's surface is frozen, said George Leshkevich, a physical scientist for the National Oceanic and Atmospheric Administration Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.

"I'm kind of surprised, actually,” he said, noting that, on average, only about one-third of Lake Superior freezes over.

Leshkevich said this year's large ice cover could affect the upcoming shipping season.

It could also mean a cooler summer. And if the ice doesn't thaw by spring, it could cause flooding.

“If the rivers … that flow into the lake [are ice-covered] ... the ice melts upstream so the water comes down, [and] has nowhere to go except over the land."

'Too early' to predict spring melt

The chair of the Lakehead Region Conservation Authority said staff are monitoring flood risk on waterways.

"But it's much too early to really tell about ... when [the spring melt is] going to occur, and how it's going to occur,” Bill Bartley said.

Bartley added that he's hoping a positive effect of the extensive ice cover will be to help raise Lake Superior's water levels to where they used to be. 

Leshkevich said water levels could rise next year because ice cover prevents evaporation.

He said the freeze is also good news for anglers and the fishing industry, because some species of fish, including whitefish, need a stable ice cover to thrive over the winter. 

"The ice cover protects the spawning beds from storms and therefore should improve the recruitment of fish in the upcoming season."

Leshkevich said the last time Lake Superior had this much surface freezing was in 1996, when almost 100 per cent of the lake was blanketed in ice.