It's all about the ice, even more significant this week with temperatures 14-degrees below zero, freezing the waters in many townships and cities on the Great Lakes (and of course in much of the eastern half of the U.S.) Detroit, especially since it is expected that they will get this treatment three times annually, according to wikipedia's Detroit page, actually lies on the Detroit River which feeds into Lake Erie.
In the image above, the city of Detroit lies just to the west of the river's debut out of Lake St. Clair (the middle splash of blue on this Landsat satellite photo.) The top of Lake Erie, one of the five Great Lakes, is shown at the bottom of the image.
Editors of The Detroit Marine Historian for the issue pictured above in black and white in February 1973 wrote in "The Log" on page 2 that: "In the 'Every little bit helps" department, the Ontario Provincial government has alloted a $7,000 grant to put the Muskoka Lakes passenger steamer SEGWUN into winter drydock. This should prevent further deterioration of the steamer-museum and permit a new chance at restoring her to active service. The Sierra Club, the national environmental and ecological advocate group, has doubts about extended navigation on the Great Lakes (emphasis mine)but this time their concern is less over the fish and other wildlife than over the men who man the midwinter fleets. Jonathan Ela, midwest Sierra representative pointed out that the danger of vessel breaking up in cold weather is greater than during the normal sailing season "and a seaman falling in would have five minutes to live."