Water levels are low enough in the Great Lakes that parts of sunken ships have become visible.
John Karl, science communicator for the University of Wisconsin Sea Grant Institute, says Wisconsin actually leads the nation in the number of shipwrecks listed on the national register of historic places. He estimates there are more than 700 sunken ships near Wisconsin, and some are well preserved because of the Great Lakes' cold, deep, fresh water.
Karl says most went down in the 19th century, when they were becoming a major vehicle for commerce.
"Those ships were made out of wood, there were no navigation facilities then, no radar, very few lighthouses at the beginning of the century, so there were all kinds of hazard including fires and storms and navigational difficulties, which caused this great number of shipwrecks on the Great Lakes," Karl says.
Karl says being a sailor in the region was extremely unsafe.
"In fact, the Great Lakes were possibly some of the most dangerous open waters to travel in the world. They're considered to be even more dangerous than open water of ocean travel, because of the shoreline all around. One of the main hazards of shipping is running aground," Karl says.
According to Karl, Wisconsin and other states now prohibit people from taking items from sunken ships. They are considered historic sites and tombs to be respected.