Think of it as a crop circle, but in a river.
A curious formation that's getting attention in Greater Portland is actually a spinning ice disk that is roughly 91 metres wide.
The formation in the Presumpscot River was widely shared on social media and has drawn comparisons to an alien spacecraft, a carousel and the moon.
The oddity drew a crowd that stood mesmerised by the slow-turning disk Tuesday afternoon in Westbrook.
The ice formation is believed to have formed naturally in a part of the river where there's a circular current that creates a whirlpool effect, said Tina Radel, the city's marketing and communications manager.
Locals say they've seen smaller ice discs before, but nothing like this one, Radel said.
Rob Mitchell, who owns a nearby office building, spotted the alien-looking disk Monday morning and immediately notified the city.
Officials say the disc is spinning slowly counter-clockwise, and has served as a big raft for ducks and other birds. "The ducks were rotating on this big Lazy Susan," Mitchell said.