This is a sunken boat near the Holy Cross Church in Marine City, which is supposed to be a rum runner. There is not much left of this wreck. There is an engine and a few scraps of wood that are visible, but there is probably more wood buried in the river bottom. I would describe the engine as “automobile sized”, and it has a flat head (no overhead valves). It’s been picked over and covered in zebra mussels.
There are plenty of newspaper accounts of rum running activities in and around Marine City, including the March 1929 shooting and killing of a U.S. Border Patrol officer stationed in Marine City, by a Canadian rum runner and a 19-year-old accomplice from Marine City. Also in June 1929, there were seven captured rum runner boats that were towed to Marine City, the final disposition was unknown at this time, but there are accounts from downriver of captured rum runner boats that were set on fire and pushed out into the river to burn and sink as standard procedure, in order to prevent them from being used as rum runners again in the future. Could this wreck be one of the seven boats? Or another one that met a similar fate?
Wikipedia claims that 75% of all the prohibited alcohol in the United States was smuggled across Lake St. Clair and its two connecting rivers.