Giant ice circle appears on NWT lake

A rotating circle of ice thought to be around 200 metres in diameter has appeared on a lake north of Fort Smith in the Northwest Territories.

Ice circles are an unusual natural phenomenon whereby circular slabs of ice begin to spin in the middle of lakes and rivers, ordinarily sculpted by the force of nearby eddy currents.

Fort Smith resident Karl Cox discovered the circle while examining satellite photos following reports of high water levels causing damage along the Taltson River,


Cox was checking to see whether high water might be affecting a camp at Tsu Lake, some 100 km north of Fort Smith, when he first noticed a grainy image of what appeared to be an ice circle.

Having had the phenomenon confirmed by local pilots, he took a flight of his own to observe and document the ice circle on Tuesday.

Ice circle on Tsu Lake
Karl Cox annotated this photograph to estimate the size of the ice circle.

Cox estimates the circle to be between 196 and 202 metres across. He believes that makes it among the largest ever documented.

“I looked at a few articles and they were talking about how one could be the biggest in the world, and it was only 100 metres or whatever,” Cox told Cabin Radio.

“Then I clued in that this one is way bigger.”


Cox was particularly keen to confirm that the circle was rotating, a key feature of the phenomenon. Annotated photos he shared with Cabin Radio appear to show the circle rotating over time.

“They’re rare, but they definitely do happen,” he said of the circles. “I’ve seen pictures of them a couple of times before.”

How the ice circle initially appeared in January 2021 satellite imagery
How the ice circle initially appeared in January 2021 satellite imagery.
Ice circle on Tsu Lake
The ice circle in February 2021. Photo: Karl Cox

Ice circles crop up in the news on average once every year or two. Recently, an ice circle in a Maine river garnered worldwide media attention.

That one was only around 90 metres in diameter, however.


“I’m going to try later in March to get out there by snowmobile,” said Cox, who hopes to film the ice circle and capture a timelapse of its movement.

“We’ll see if it’s still there or not.”