SUPERIOR, Wis. -

Ships using Lake Superior are having a tough time due to the worst buildup of ice in decades.

The National Weather Service started tracking freeze-ups in 1978, and says this is the second-fastest and thickest ice-up in 35 years, according to Wisconsin Public Radio News. Coast Guard Soo Vessel Traffic Director Mark Gill said this is the worst since 1989.

"Christmas Eve was the first sign of trouble," Gill said. "It got to the point that we're not able to take ships down there anymore because the ice is so thick that it's pressed to the bottom."

A trip from Duluth, Minn., to Gary, Ind., that normally would take three days now takes six to seven, Gill said.

The down-bound lane on the St. Mary's River connecting Lake Superior with the lower lakes is closed. Gill said they use another measuring stick called "freezing degree days" — the number of degrees below freezing each day. He says they used to close the locks when that number reached 500.

"Using the old standards of closing the locks at 500 freezing degree days, we would have closed the locks the Monday before Christmas," Gill said.

Many ships on the Great Lakes are tying up early for the winter, Gill said. The Soo Locks close Wednesday.