Just about every type of boat or ship you can imagine — from wooden canoes to mine-laying submarines — has deployed on the Great Lakes at some point in time. And this is to say nothing of the naval battles that broke out here during the War of 1812. So it's not surprising that the lakes contain an estimated 8,000 shipwrecks, with new ones being discovered on a regular basis.
Quantity is nice, but so is quality. Many of these vessels are almost perfectly preserved. The Great Lakes contain cold, fresh water. That allows shipwrecks to last longer than they would in the ocean. In saltwater, iron-based metal corrodes more rapidly. Also, the ocean's home to shipworms that feast on wooden wrecks. Finally, there's coral, which thrives in warm waters and can encrust itself all over submerged vessels.
Conditions in the Great Lakes make it a lot easier for archaeologists to study shipwreck sites. There are also strict anti-looting laws which help prevent the artifacts on these ships from being stolen. However, that being said, there's still one big threat to the sunken vehicles: Invasive zebra mussels. It's thought that when the mollusks latch on to boat hulls, they end up damaging wooden and metallic wrecks alike. The situation has historians scrambling to document important ships before too much harm befalls them.