The Fitz is the last and largest of hundreds of ships that have gone down in Lake Superior from the early 1800's. More about some other famous wrecks can be found at the Great Lakes Shipwreck Museum where they keep the Fitzgerald's bell as a memorial. There is a site for the ship with a lot of information including a timeline.
Lake Superior is the largest freshwater lake in the world if you go by surface area. It is incredibly deep for a lake and the water is extremely cold. It's cold enough to inhibit the bacteria present with normal decomposition and so the lake preserves and often keeps what sinks there. The song sings about how Superior never gives up her dead and that would be why. The lake is large enough that it impacts the local climate's temperature and snowfall totals. It can be placid like in the photo I took a couple of summers ago.
Or it can be really rough like in this photo taken by Greg Kretovic.
Growing up, I lived within an hour's drive of the Lake Superior shoreline. I was just a kid in 1975 and can't remember hearing about the Fitz sinking until later but I do remember the gale and the damage it did to buildings in our area at the time. The loss of the Fitz is one of those events that stays with the local people like the Kennedy assassination or the Challenger disaster. It comes complete with competing theories about why the ship went down. No one knows for sure except Captain McSorley and his crew of 28, may they rest in peace.
Fair winds and following seas to all those who work on the water.
...for the sea is so wide and our ship is so small