The Big Bay Sloop consists of the remains of a small unidentified sloop off the coast of Madeline Island's Big Bay in Lake Superior. As a sloop, this vessel represents a rare example of a once common vessel type on the Great Lakes: the small working boat. There is a virtual absence of documentation of small craft on the Great Lakes, both for commercial and personal purpose. This makes identification of small Great Lakes craft a particularly difficult task.

The vessel was originally believed to be a Huron boat, but its diagnostic features fit neither the description of a Huron boat nor a Mackinaw boat. The construction, wire rigging, and metal cleat plate indicate an approximate build date of between 1880 and 1920. The Apostle Islands were developed as a popular vacation destination during the nineteenth century; it is therefore possible that the Big Bay Sloop was used for leisure. The vessel's association with an isolated, unfinished log crib, however, suggests the vessel was used for commercial purposes at the time of its loss.
The Big Bay Sloop rests in 25 feet of water within Madeline Island's Big Bay, approximately 300 feet east of Big Bay State Park. It was discovered in the 1990s and was originally identified as a Huron boat. A non-disturbance archaeological survey, as well as a survey of historic records, failed to positively identify the vessel type or name, but suggests the vessel is a type of vernacular sloop rather than a Huron boat. The Big Bay Sloop site is the only one of its type known to exist in Wisconsin waters, making it a significant archaeological resource.

The vessel lies upright on a sand bottom. Its bow is the most intact, with the stem and much of the outer hull planking and frames extant up to the deck level. A large section of the foredeck is extant but has collapsed into the hull. Much of the lower hull is filled with rock. The sand was probed in several locations around the centerboard trunk, and in nearly all locations, rock was discovered a few inches below the surface of the sand. This suggests the vessel was intentionally filled with rock at the time of loss, either as cargo or ballast.

An intriguing feature of the Big Bay Sloop site is a large log crib, measuring nearly 9 feet wide and 23 feet in length, that lies immediately north of the vessel's bow. Several tree trunks and stumps have been caught by the crib, lying within and around it. A search of the surrounding area did not reveal any other features associated with a pier or breakwater, making the isolated crib an anomaly.