INDIANAPOLIS (AP) — U.S. and Canadian Coast Guard crews kept up their battle Monday to clear pathways for vessels hauling vital raw materials on the ice-clogged Great Lakes, where a shipping logjam forced a weeklong shutdown of the nation’s largest steel factory.

Traffic remained largely at a crawl after a winter that produced some of the heaviest ice on record across the five inland seas, where more than half the surface area remained solid this week. Icebreaking ships slogging across Lake Superior were still encountering ice layers 2 feet to 3 feet thick. In some areas, wind and wave action created walls of ice up to 14 feet high.