This 30-second exposure shows the circular ice floe spinning counter-clockwise Monday in the Presumpscot River below Bridge Street.

In a photo taken by a drone, a disk of ice spins in the Presumpscot River in Westbrook on Monday. The circular sheet of ice drew comparisons to a crop circle and a Lazy Susan.

Curious observers watch the rotating disk of ice Tuesday on the Presumpscot River in Westbrook. One theory of how it formed: The flow of the river is pushing the ice disk along like a paddle wheel as ice builds up on the edges.

A crowd gathers at the now motionless disk of ice on the Presumpscot River in Westbrook on Wednesday. Police stopped a man who attempted to walk out onto it.

On Wednesday, the disk of ice on the Presumpscot River in Westbrook was lodged against ice on the bank. With temperatures expected to be in the single digits overnight, and snow in the weekend forecast, a meteorologist suspected the disk may not survive the week.

Pat Mahoney of Gorham watches the now-motionless disk of ice on the Presumpscot River in Westbrook. The phenomenon was still drawing crowds Wednesday.

Andrew Sims, a photographer from Freeport, ventures out in the Presumpscot River in Westbrook to free the ice disk so he can record a “nice time-lapse” of it in motion Thursday.

Andrew Sims, a Freeport photographer, freed the Westbrook ice disk. He is holding a drone.

People gather to watch the ice disk spin after Andrew Sims, a photographer from Freeport, ventured out in the Presumpscot River in Westbrook on Thursday to free the ice, which had become stuck against the riverbank.