The Straits of Mackinac, which are also referred to as the Mackinac Strait, Michillimacinac Strait, Strait of Maciknac, or Straits of Mackinaw, are waterways in the US state of Michigan. A strait is a narrow waterway that connects two larger bodies of water, often between two large landmasses, which may or may not be navigable, and is normally formed by natural means. The Straits of Mackinac are located between the Lower Peninsula of Michigan and the Upper Peninsula of Michigan, and connect Lake Michigan and Lake Huron, which are both Great Lakes of North America. The main strait has a width of approximately 3.5 mi and a maximum depth of 295 ft.
French colonists established a mission in St. Ignace in 1671, and later built a military fort, named Fort Michilimackinac, along the straits in 1715. In 1781, A British fort, named Fort Mackinac, was built on Mackinac Island, which replaced France's Fort Michilimackinac. The straits are named after the island, which the indigenous population referred to as Mitchimakinak, meaning "big turtle," but was shortened by the British to Mackinac.
Historically, the Straits of Mackinac served an indigenous fur trade route, and later as an important shipping lane for goods, such as iron ore, and people, despite the narrowness and shallowness of the straits. Tofay, icebreakers are used during freezing winters to ensure navigation is possible throughout the year. Mackinac Bridge was constructed at the narrowest point of the straits, which now provides a crossing for vehicles. Prior to the bridge, ferries were needed to transport people and vehicles, but since its construction ferries now carry only people to Mackinac Island. Other islands in the Straits of Mackinac include Bois Blanc, which is inhabited, and Round Island, which is uninhabited.
A pipeline owned by Enbridge Inc., named Enbridge Line 5, runs near the Mackinac Bridge. The pipeline dates back to 1953 as an extension of the Interprovincial Pipe Line Company line that transports oil from the Canadian province of Alberta to Lake Superior. Enbridge Line 5 goes into the straits near the northern shore at St. Ignac, Michigan, and has a current daily capacity of about 540,000 barrels. At the time of the pipeline's construction in 1953, developers convinced the local population to allow its construction by claiming the line would increase the United States' national security, as well as the security of North America overall. Legislation to create the Mackinac Straits Corridor Authority was signed in 2018, which would oversee the building of a tunnel to hold the Enbridge Line 5 pipeline beneath the lake bed.
The Straits of Mackinac are monitored and patrolled by a unit of the United States Coast Guard (USGC) that is based in Graham Point, St. Ignace. The Coast Guard is also responsible for keeping the straits navigable throughout the year, which it does with the help of the USCGC Mackinaw, a Great Lakes icebreaker that has been in operation since 2005 and is based in Cheboygan, Michigan. Lighthouses along the strait include McGulpin Point Light, Round Island Light, and Old Mackinac Point Light.