This U.S. Coast Guard photo shows a convoy of Great Lakes cargo ships lined up to follow an icebreaker on the St. Marys River, which links Lakes Superior and Huron. Much of the lakes’ surface is frozen. (The Minnesota Star Tribune)

The U.S. Coast Guard will begin breaking ice Tuesday in the Duluth-Superior Harbor, setting the stage for what promises to be a tough start to the Great Lakes shipping season.

Thanks to early, bitter and lasting cold, Lake Superior is more covered by ice than it has been in two decades. By Monday, 95.5 percent of Lake Superior's surface was covered by ice of varying thickness, according to data from the Great Lakes Environmental Research Laboratory.

The average ice coverage across all five lakes hit 90.5 percent — the high so far this winter. That pulls the lakes closer to the record of nearly 95 percent set in February 1979.

"We have a lot more ice than we have ice breakers," said Mark Gill, director of vessel traffic services for the Coast Guard at Sault Ste. Marie. "It'll be slow."

A 225-foot cutter will create fractures in the ice in areas used for ice fishing, snowmobiling and other recreation — including the Superior Front Channel and the area next to Minnesota Point in Lake Superior. The Coast Guard is recommending that anglers remove their ice shacks and equipment.

The shipping season is marked by the opening of the Soo Locks at Sault Ste. Marie on March 25. Usually, by that time "there are ships lined up in both direction to go through that ice," Gill said. But that's less likely this year, because breaking ice beforehand could take longer.

"Patience is kind of the message we're offering to the U.S. and Canadian shipping industries," he said.

A cool March could add to this year's big ice concentrations. "If it stays cold, the ice will grow thicker," Gill said. "That's a problem for us."

Jenna Ross • 612-673-7168

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Jenna Ross

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Jenna Ross is an arts and culture reporter.