WESTBROOK, Maine (CBS Local) — A massive disc of ice has formed in the Presumpscot River in Westbrook, Maine, a suburb of Portland. Tina Radel, Westbrook’s marketing and communications director, posted images of the Westbrook Ice Disc on social media, saying the ice is slowly rotating counter-clockwise and that birds have been using it as a resting area.

“It looks like the moon has landed in Westbrook!” the city wrote on Facebook Tuesday morning.

No exact measurement of the Westbrook Ice Disc has been taken, but in video shot from a drone and shared by the city, it appears larger than two nearby downtown buildings.

Westbrook resident Adam Farnsworth also documented the Westbrook Ice Disc with a drone and shared it on Facebook.

Ice discs like the one in Maine are not uncommon when atmospheric conditions are just right, the Bangor Daily News reports.

Citing a 2009 Daily Mail report, the newspaper says 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” and “as the disc rotates it grinds against surrounding ice, smoothing into a perfect circle.”