Lake freighters, or lakers, are bulk carrier vessels that ply the Great Lakes. These vessels are traditionally called boats, although classified as ships.Lakers carry bulk cargoes of materials such as limestone, iron ore, grain, coal or salt from the mines and fields to the populous industrial areas down the lakes. The 63 commercial ports handled 173 million tons of cargo in 2006. Because of winter ice on the lakes, the navigation season is not usually year-round.