Lakes Michigan and Huron are connected by the Straits of Mackinac, a channel that separates the upper and lower peninsulas of the state of Michigan. Immediately to the north, the St. Marys River connects Lake Superior to Lake Huron. This small region was therefore a critical meeting place for Native American communities that traveled by small watercraft. As Europeans traveled to the upper Great Lakes, the area became an important settlement and transportation node.

The Straits of Mackinac are relatively easy to transit by boat. There are no rapids and, when weather is good, the passage between Lakes Michigan and Huron is easy to navigate. As a result, freight and passenger traffic flourished through the Straits, particularly as Chicago, Milwaukee, and other Lake Michigan port cities prospered.

The connection between Lake Superior and Lake Huron was more difficult. Rapids made the St. Mary’s River impassable to all but the smallest boats. This delayed the development of maritime commerce into Lake Superior. Canals were built around the rapids, then rebuilt as the size of ships attempting to travel to Lake Superior increased. Today, the Soo locks (named for the phonetic spelling of the cities of Sault St. Marie, Michigan and Sault Ste. Marie, Ontario) can accommodate freighters over 1000 feet long.