The designation applies to some 600,000 square miles of waters as far away as American Samoa and, nearest to Maryland, in the Atlantic just off the coast of North Carolina. Some, like the Mallows Bay proposal, aim to preserve and commemorate important maritime history, like a mile-wide column of water off the coast of North Carolina. It preserves the wreckage of the USS Monitor. a Civil War vessel. The Thunder Bay National Marine Sanctuary in Lake Huron contains the remnants of two steamships dating to the late 1800s and early 1900s, the Ohio and the Choctaw.