Mackinac Bridge Swim

Looking up at the soaring steel towers of the Mackinac Bridge while treading water in the Straits of Mackinac offers a monumental perspective granted to very few swimmers. The Mackinac Bridge Swim is an open water crossing across the deep freshwater channel separating Michigan's Upper and Lower Peninsulas, organized by I Swim for Amy INC in July. Swimmers take to the open water beneath one of the world's most famous suspension bridges, completing an epic journey across the threshold where two Great Lakes converge.

The crossing beneath Mighty Mac: Mackinaw City to St. Ignace

Swimmers set off from the southern mainland at Mackinaw City and chart a 4.5-mile course across the open strait to finish at Bridgeview Park in Saint Ignace. Conceived as an organized group swim rather than a timed competition, the event operates as a dedicated fundraiser supporting first responders across Michigan. Without the rush of a timing clock, the entire focus rests on navigating the deep lake waters alongside fellow open water enthusiasts. Safety demands strict preparation, as the water temperature in the straits generally fluctuates between 57 and 70 degrees. Every participant is required to wear a wetsuit and tow a high-visibility swim buoy, with entry open to swimmers aged 14 and older who qualify by demonstrating an authenticated pace of 40 minutes per mile or faster.

At the start line, swimmers are organized into heats designated by colored swim caps—white for the steadier pacers, blue for the mid-pack, and red for the fastest—ensuring a smooth release into the rolling waters. The open strait regularly tests technique, with participants in past editions contending with hazy weather and choppy whitecap waves reaching four feet in height. Looking up from the crest of a swell, the massive towers and suspension cables dwarf every stroke. Approaching the northern shoreline, water temperatures can drop sharply like meeting an icy wall, yet the current eases as you approach the causeway and the water feels like a warm bath the moment you step ashore.

The Straits of Mackinac: where two inland seas collide

The Straits of Mackinac form a vast waterway five miles wide and up to 90 meters deep, linking Lake Michigan and Lake Huron into a single hydrological basin. The strait acts less like a simple outlet and more like a pulsing channel between two immense inland seas. Even on calm days, the aquatic environment feels untamed and vast. Beneath the surface lies a complex hydrodynamic puzzle, with currents that reverse direction approximately every day and a half. Driven by atmospheric pressure and seiches sloshing between the lake basins, water volume surging back and forth through the gap can exceed 75,000 cubic meters per second. These powerful volume shifts keep the water constantly stirred and invigorated, creating a lively environment for swimmers to read and navigate. The submarine topography tells an ancient story. Thousands of years ago, when lake levels sat much lower, the proglacial Lake Chippewa and Lake Stanley were connected through the deep Mackinac Channel.

Old Mackinac Point and the keepers of the Straits

Long before modern bridges and navigation towers arose, the indigenous Ojibwa maintained shore fires along the straits. The surrounding waterway is historically unforgiving to maritime traffic, preserved today within the Straits of Mackinac Shipwreck Preserve, which shelters numerous sunken vessels on the lake bed. To aid mariners, McGulpin Point Light was erected in 1869 about five kilometres west of the race area, surrounded by 336 feet of Lake Michigan shoreline. For decades, the lighthouse keeper James Davenport provided essential observations on ice pack conditions each spring, signaling when the straits were clear enough for commercial shipping to resume after freezing solid during deep winter. About three kilometres from the starting area stands Old Mackinac Point Light, its 45-foot cylindrical tower constructed from Cream City brick and Indiana limestone upon a solid ashlar foundation.

The station was famed for a steam-driven fog signal that once consumed 52 cords of stove wood in just two weeks of heavy weather, guiding iconic railroad car ferries like the SS Chief Wawatam and SS Sainte Marie through zero-visibility conditions across the passage.

Mackinac and St. Helena: from Devil's Kitchen to island shoals

Mackinac Island is an ancient limestone landmass sculpted around 13,000 BC by melting glaciers atop bedrock that dates back more than 400 million years. Indigenous fishermen frequented its shores as early as AD 900. Across the island are breathtaking geological monuments, such as Arch Rock perched 146 feet above the ground, and the stacked caverns of Devil's Kitchen, carved out of brecciated limestone cliffs by Lake Huron waves during the post-glacial Nipissing epoch. Looking west into the Lake Michigan approach, about eleven kilometres from the crossing, lies St. Helena Island. Covering 240 acres, the island features a sheltered natural harbor along its northern shore that offered ships safe haven during southwesterly gales.

However, shallow shoals extending into the channel proved hazardous, prompting the construction of a lighthouse in 1872 that later became the first in Michigan to be automated using an inventive sun-valve system. Nearer the span, just one mile west of the Mackinac Bridge and south of Point La Barbe, sits uninhabited Green Island. Spanning roughly 16 acres of dense thickets and windswept trees, it remains a quiet natural outpost tucked into the Lake Michigan currents.

St. Ignace waterfront: boardwalks, dunes and island ferries

At the end of the crossing, swimmers step ashore at Saint Ignace, a historic lakefront city located where Lake Huron meets Lake Michigan. The downtown boardwalk hugs the shoreline, offering open vistas toward Mackinac Island while connecting directly to the St. Ignace City Marina, home to local restaurants, shops, and dockside activity. The surrounding coast features rocky sandstone ledges shaped by long cycles of Great Lakes erosion. A short scenic drive leads to expansive sand dunes along Lake Michigan, perfect for relaxing on the soft sand or taking an easy recovery dip in the open freshwater. It is the ideal vantage point to rest tired shoulders, look back at the grand bridge spanning the horizon, and savor the crossing.