This is a great article on the winter's impact on the Great Lakes shipping companies as well as the indirect impact on the companies that rely on the products shipped via the Great Lakes.
Read the full article here: http://www.nytimes.com/2015/03/24/business/deep-freeze-on-great-lakes-halts-cargo-shipments.html?_r=0
Shipping is usually up and running again by March. But the opening of the St. Lawrence Seaway, the critical system of locks that connects the Atlantic Ocean to the Great Lakes, has been postponed until April 2. Even when the locks open, there is no assurance that all of the lakes, particularly choke points prone to ice buildup, will be navigable.
Last year’s ice-induced delays reduced early shipments from the United States by seven million tons, according to the Lake Carriers’ Association, which represents American shipowners. That amounts to about 10 percent of all American shipments on the lakes.