A tractor broke through the ice on the pond at Deering Oaks in Portland on Monday in what the city has described as a normal occurrence.

The machine was clearing snow from the pond, a popular spot for ice skating, when the ice cracked and it fell through, city spokesperson Jessica Grondin said in an email Tuesday morning.

“This has happened many times before and is why we don’t put machines on deeper ponds, like Capisic Pond,” she said, noting it is fairly easy to pull the machines out of the pond at Deering Oaks because it is only 3 feet deep.

And because the pond is so shallow, Grondin said, there was no danger to the operator.

City staff measured the ice to make sure it was 8 inches thick before driving the equipment onto the pond, but “obviously there is variable thickness,” Grondin said.

She said that even though using larger equipment increases the risk of the machine falling into the pond if it encounters thinner patches of ice, city staff continue to use the larger equipment because it is more efficient at clearing snow. She said that smaller equipment like snow blowers are used when the ice is found to be too thin to support the larger machinery.

Staff Writer Grace Benninghoff contributed to this report.