It happened Wednesday evening on Metropolitan Parkway just east of L'Anse Creuse Street.
The sheriff's office says a married couple from Clinton Township stopped in the left lane after their boat trailed became disconnected, and got out of their car to try and hook the trailer back up.
The sheriff's office says a 21-year-old man apparently didn't see that the trailer had stopped, and crashed into the back of it. The force caused the boat to dislodge, and the husband, 29-year-old William Rainey III, was pinned underneath.
The 21-year-old's vehicle also then caught fire.
Rainey was taken to the hospital, where he was pronounced dead. His wife and the driver of the other vehicle were treated for non-life threatening injuries.
The sheriff's office says alcohol does not appear to be a factor at this time.