FREDERICTON, N.B. -- An ice jam four kilometres long on the St. John River at Perth-Andover, N.B., is creating flooding concerns along the western part of the province near the border with Maine.

The ice jam already flooded part of Route 105 leading to the Tobique First Nation on Monday and prompted the closure of three schools in the area.

"Ice jams are such unpredictable things," Geoffrey Downey, spokesman for the provincial program River Watch, said in an interview Monday. "They form and then they let go when they let go."

"There's nothing you can really do about them on the St. John River. You just have to wait them out and hope the impact isn't too severe when the water works its way around," he said.

Ice jams occur when pieces of ice along a river clump together and block the water from flowing. When the ice finally begins moving, the backed up water can rush through, causing flooding. Downey said a mobile command post has been set up in the region as officials keep an eye on the ice movement.

At one point over the weekend, the ice jam at Perth-Andover measured about eight kilometres in length, but Downey said it has compressed to about four kilometres long. He said there are smaller ice jams at Sainte-Anne-de-Madawaska and Hartland, in the western part of the province.

Downey said heavy rains over the weekend in southern New Brunswick increased currents in some rivers and streams, forcing two vehicles off the road.

In one case a culvert was washed out north of Moncton, while the other saw a truck pushed off the road by floodwaters near Sussex. He said a man had to be rescued by boat from the roof of the truck.

Downey said people need to act responsibly near the river banks.

"We don't need people doing the disaster tourism thing and driving to Perth-Andover to look at the massive ice jam and take pictures walking next to it and walk down the river banks," he said. "People need to really respect the river systems right now."

Police in Saint John on Monday cautioned motorists about hydroplaning because of the water on the roads.

This report by The Canadian Press was first published March 29, 2021.