A giant ice disk is floating in the Presumpscot River in Westbrook. Credit: Troy R. Bennett

A huge ice disc has formed in the Presumpscot River in Westbrook, Portland television station CBS 13 reported.

The attention-grabbing formation is spinning counter clockwise and has served as a big raft for local birds, the TV station posted.

Credit: Troy R. Bennett

The discs “occur at bends in the river where the accelerating water creates a force called ‘rotational shear,’ which breaks off a chunk of ice and twists it around,” the Daily Mail once reported, when one of the circles was seen in Great Britain for what was believed to be the first time in 2009. “As the disc rotates, it grinds against surrounding ice, smoothing into a perfect circle.”

According to media reports, the largest ice disc recorded was a 160-foot circle in Sweden’s Pite River in 1987.

No measurement of the Westbrook ice disc has been published, but in a photograph posted on social media by the city, it appears larger than two nearby downtown buildings.

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Seth has nearly a decade of professional journalism experience and writes about the greater Portland region.