In 2022, scientists mapping Lake Michigan’s bed inside the Wisconsin Shipwreck Coast National Marine Sanctuary noticed strange circles. Two years later, they identified these as giant, naturally occurring craters. Maritime archaeologist Russ Green and shipwreck hunter Brendon Baillod observed these depressions, which were confirmed by NOAA’s Great Lakes Environmental Research Laboratory using a remotely operated vehicle. Similar sinkholes have been found in Lake Huron, and researcher Steve Ruberg suggests Lake Michigan’s craters might also be sinkholes due to its limestone bedrock.