The Straits of Mackinac connect Lake Michigan and Lake Huron at the narrow channel between the Upper and Lower Peninsulas of Michigan, and Chris Izworski tracks it as a distinct sub-region because it is the single point where the two largest Great Lakes meet as one hydraulic system. The straits, the Mackinac Bridge, Mackinac Island, Bois Blanc Island, and the surrounding shoreline of St. Ignace, Mackinaw City, and Cheboygan form one of the most distinctive shoreline sub-regions on the Great Lakes, with currents that reverse direction in response to wind, vessel traffic that includes a substantial share of the entire Great Lakes commercial fleet, and shoreline that supports one of the most heavily visited tourism destinations in the upper Midwest.
Sub-region: Straits of Mackinac, connecting Lake Michigan and Lake Huron.
Major communities: Mackinaw City, St. Ignace, Mackinac Island, Cheboygan, Bois Blanc Island.
Lake datum: 577.50 feet IGLD85, the Lake Michigan-Huron datum (shared by both lakes).
Anchor years: 1986 cycle high, 2013 modern low, 2020 record monthly high at 581.70 feet.
Bridge: Mackinac Bridge, completed 1957, 5.0 miles total length, 552-foot main span clearance above water.
Currents: reversible bidirectional flow driven primarily by wind, with measurable but variable mean flow.
Lake Michigan and Lake Huron are hydraulically the same lake at the Straits, sharing a single basinwide level (the Michigan-Huron datum of 577.50 feet IGLD85) and connected by the open channel of the Straits. The live dashboard on the homepage reports the shared level. The distinctive hydrologic behavior at the Straits is the bidirectional current that responds to wind: sustained west and southwest wind drives water from Lake Michigan toward Lake Huron through the Straits, while sustained northeast and east wind reverses the flow. The mean residual flow is small, but the short-term current can run several feet per second in either direction.
The 2019 to 2020 high cycle tested shoreline along the Straits in the standard ways the rest of the Lake Michigan-Huron system did, with beach narrowing at Mackinaw City and St. Ignace, dock and ferry infrastructure stress at the Mackinac Island ferry harbors, and bluff exposure along the more natural shoreline segments. The Straits are unusual in the Great Lakes for the high concentration of historical and tourism infrastructure that interacts with the modern shoreline, including Fort Michilimackinac, the lighthouses at Old Mackinac Point and McGulpin Point, the Mackinac Bridge approaches, and Mackinac Island's harbor and historic waterfront.
Mackinaw City and the Lower Peninsula approach at the south end of the Mackinac Bridge includes the city of Mackinaw City, Colonial Michilimackinac State Park, the Mackinac Bridge south approach, and the lighthouses at Old Mackinac Point and McGulpin Point. Property density is high along the waterfront with substantial tourism infrastructure including marinas, ferry terminals, and the historical sites that draw millions of visitors per year.
St. Ignace and the Upper Peninsula approach at the north end of the bridge includes the city of St. Ignace, the Mackinac Bridge north approach, the Father Marquette National Memorial, and the ferry terminals for service to Mackinac Island. The St. Ignace waterfront is comparably developed to Mackinaw City but with the additional commercial and industrial waterfront that supports Upper Peninsula tourism and freight movement.
Mackinac Island sits in the Straits roughly three miles east of the Mackinac Bridge and is one of the most distinctive tourist destinations in the Great Lakes. The island has a year-round resident community of roughly 500, no automobile traffic on the island itself, and a heritage tourism economy that draws visitors throughout the May-to-October season. The island's harbor and the federal ferry-service operations connect it to St. Ignace and Mackinaw City.
Bois Blanc Island sits east of Mackinac Island and is the largest island in the immediate Straits area. Bois Blanc has a much smaller permanent population than Mackinac Island, very limited tourism infrastructure, and substantially undeveloped shoreline. The island is connected to the mainland by ferry from Cheboygan.
The Cheboygan corridor south of the Straits includes the city of Cheboygan, the federal harbor and Coast Guard station at Cheboygan, and the Inland Waterway entrance from Lake Huron to the inland lake system at Mullett Lake, Burt Lake, and Crooked Lake. The Cheboygan River connects the Inland Waterway to Lake Huron through the federal harbor.
The Michigan OHWM at 581.5 feet IGLD85 applies along the Michigan portions of the sub-region under NREPA Section 32502. Mackinac Island has additional regulatory layers from the Mackinac Island State Park Commission, which administers the substantial public-land portion of the island under state authority. Federal jurisdiction applies at the Mackinac Bridge, the Coast Guard stations, and the federal harbors.
The distinctive property-owner concern at the Straits is the interaction between high water, ice cover during winter, and the substantial maritime traffic that transits the Straits year-round. The Straits remain partially or fully ice-covered in many winters, with U.S. Coast Guard icebreaker operations maintaining the navigation channel. Ice push during freeze and breakup is a meaningful exposure for unprotected shoreline at Mackinaw City, St. Ignace, and along the more natural shoreline segments.
For a current reading, see the live dashboard. For broader context, the Straits are the meeting point of Lake Michigan and Lake Huron. For neighboring Lake Huron sub-regions, see Sunrise Side, North Channel, and Georgian Bay. For neighboring Lake Michigan sub-regions, see Beaver Island and Northwest Michigan.
For broader Great Lakes shipping context including vessel transits through the Straits, the Great Lakes Gazette daily maritime brief covers the commercial fleet activity that defines much of the Straits traffic pattern.