The deep, cold fresh waters of the Great Lakes seem to provide the best environment for the preservation of old shipwrecks. The latest example is the 1780 wreck of the British warship HMS Ontario recently found at the bottom of Lake Ontario. According to this report the ship is the oldest wreck ever found in the Great Lakes and is in an excellent state of preservation.
I thought this picture was kind of a teaser and have been looking for more. Let me know if you guys find any.