DULUTH — A U.S. Coast Guard cutter has started ice breaking activities in the Twin Ports of Duluth and Superior, an annual ritual that signals the approach of spring.

The cutter Alder began cleared the channels Tuesday for the upcoming shipping season. It’s so the 1,000-foot long ships loaded with taconite, coal, limestone and other cargo can maneuver through without getting stuck.

Minnesota Public Radio News says the Coast Guard is also responsible for maintaining the ports in Two Harbors and Silver Bay and may help break ice in the Thunder Bay, Ontario harbor.

The Great Lakes shipping season begins March 25 when the Soo Locks open between Lake Superior and lakes Huron and Michigan.

High water levels have delayed the opening of the St. Lawrence Seaway on the eastern side of the lakes by two weeks.