Mackinac Bridge Opened in 1957, this 5 mile long bridge has a central suspension supporting the roadway 200 ft off the water using 552 ft Main towers. The suspended section of roadway is a little over 1.6 miles in length. The depth of water at midspan is 295ft with a shipping clearance of 155ft and a favorite of the local ducks. View from the Old Mackinac Point Lighthouse Mackinaw City, MI.