Mackinaw City sits at the southern end of the Mackinac Bridge at the meeting of Lake Michigan and Lake Huron, and it is one of the most hydrologically interesting places in the Great Lakes basin. The Straits of Mackinac are the open channel through which Lake Michigan and Lake Huron exchange water continuously, which is why limnologists treat the two as a single hydraulic system. I am Chris Izworski. I live in Bay City, I cross the bridge more often than I want to count, and I have spent enough days at Mackinaw City between ferry trips to Mackinac Island and Saint Ignace to take the local water level picture as its own coherent place. This page is the orientation.
Lake Michigan and Lake Huron share a single water surface. The Straits of Mackinac are five miles wide and roughly 250 feet deep, which is wide and deep enough that the two lakes equilibrate continuously. The chart datum and the long-term mean are the same for both. The Mackinaw City NOAA station, 9075080, is the official Straits gauge and is the reference I use for any Mackinaw City, Saint Ignace, Mackinac Island, or northern Lake Huron and northern Lake Michigan question. There is a separate Saint Ignace gauge that reads almost identically and is useful as a cross-check.
The implication for property owners in Mackinaw City is that the lake stage at home is the same stage that drives Bay Harbor, Charlevoix, Petoskey, and Beaver Island on the Lake Michigan side, and the same stage that drives Cheboygan, Alpena, and the entire Sunrise Coast on the Lake Huron side. Mackinaw City sits at the hydraulic center of the lower lakes.
The Mackinac Bridge crosses the Straits with a main span clearance of 155 feet above the water at chart datum. Lake level variation through the historical envelope shifts the actual clearance by several feet in either direction. At the 1964 record low, the bridge had several feet more clearance than at chart datum. At the 1986 and 2020 high stands, the bridge had several feet less. For commercial vessel operators, the 155-foot air draft figure is conservative because it assumes mean lake level, but the variation is meaningful for the tallest lakers passing through the Straits. The Mackinac Bridge Authority publishes current clearance information based on the prevailing water level.
Three ferry lines operate between Mackinaw City, Saint Ignace, and Mackinac Island. The ferry docks at Mackinaw City have been progressively modified through the recent extremes. In low water cycles, draft restrictions affect approach speeds and require channel awareness near the breakwater entrances. In high water cycles, the dock surfaces themselves contend with wave wash from southwest blows that propagate up the Lake Michigan side of the Straits. The Star Line, Shepler's, and Mackinac Island Ferry Company all post operational notices when water levels produce unusual conditions.
The Mackinaw City public beach east of the bridge fronts the Straits with a sand and cobble shore that takes the dominant west wind direction. The beach contracts visibly in high water cycles. West of the bridge, the Headlands International Dark Sky Park shoreline is a more rugged sand and bedrock coast that does not change as visibly with lake level but does take significant wave action from north and northwest blows.
The Old Mackinac Point Lighthouse on the bluff just east of the bridge tower is a useful local reference point for the long water level record. The lighthouse foundation and the surrounding pavilion area have not been overtopped in the modern record, but the beach immediately below has contracted and expanded through every high and low cycle since the structure was built in 1892. Photographs of the lighthouse beach across decades are a usable visual record of Straits water level history.
The Straits of Mackinac are exposed to long fetches in two directions, west across Lake Michigan and east across northern Lake Huron. The strongest storm events at Mackinaw City typically come from southwest blows that build wave energy across the open Lake Michigan basin and arrive at the Straits as a sustained surge plus wave event. The November 1975 storm that sank the Edmund Fitzgerald in eastern Lake Superior produced significant Straits conditions as well. The November 2018 storm event produced documented wave damage to Mackinaw City waterfront infrastructure.
I cover the Mackinac and Straits region in more detail on the Mackinac page and the wider Lake Michigan and Lake Huron pictures on the Lake Michigan and Lake Huron overviews. Questions specific to Mackinaw City can reach Chris Izworski through chrisizworski.com.