Fort Gratiot in St. Clair County, Michigan — The American Midwest (Great Lakes)

Lake Huron Water Supply Project
⎯⎯⎯
Tunnel Explosion

Registered Michigan Historic Site

Photographed by Joel S., September 19, 2015

1. Lake Huron Water Supply Project/Tunnel Explosion Marker

Inscription.
Lake Huron Water Supply Project In 1968, to serve the water needs of a growing population, the Detroit Metro Water Department began work on the Lake Huron Water Supply Project. This massive feat involved erecting a submerged intake crib connected to a six-mile intake tunnel beneath Lake Huron. The mechanical mole that dug the 16-foot wide tunnel bored through the bedrock beneath the lake at a rate of 150 feet a day. The project excavated more than one billion pounds of rock. The water treatment plant pumped clean water into an 82-mile system of water mains supplying Detroit and Flint. When finished in 1973, the $123 million system boasted a capacity of 400 million gallons a day.

Tunnel Explosion On December 11, 1971, a shotgun-like blast claimed the lives of twenty-two men working on a water intake tunnel beneath the bed of Lake Huron. A pocket of methane trapped within a layer of ancient Antrim shale fueled the explosion. An exhaustive inquiry determined that drilling for a vertical ventilation shaft from the lake's surface had released the trapped gas. A drill bit that fell ignited the gas. The blast created a shock

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wave with a speed of 4,000 miles an hour and a force of 15,000 pounds per square inch. Witnesses reported seeing debris fly 200 feet in the air from the tunnel's entrance. This tragedy resulted in stronger mining safety regulations and enforcement. It was one of the deadliest industrial accidents in Michigan history.

Erected 2011 by Michigan Historical Commission - Michigan Historical Center. (Marker Number L2219.)

Topics and series. This historical marker is listed in these topic lists: Bridges & Viaducts • Disasters • Industry & Commerce • Waterways & Vessels. In addition, it is included in the Lost at Sea, and the Michigan Historical Commission series lists. A significant historical date for this entry is December 11, 1971.

Location. 43° 4.928′ N, 82° 28.201′ W. Marker is in Fort Gratiot, Michigan, in St. Clair County. It is on Park Road east of Michigan Highway 25, in the median. The marker is in Fort Gratiot County Park. The entrance to the park is about 0.1 mile east of M-25 on Metcalf Road. The park road is unnamed, but is a loop, with the marker about 0.3 miles into the park. In season, and on certain off-season weekends and holidays, there is a $20 charge to enter the park where this marker is located—unless you are a resident of St. Clair County.

Photographed by Joel S., September 19, 2015

2. Lake Huron Water Supply Project/Tunnel Explosion Marker

Touch for map. Marker is at or near this postal address: 3325 Lakeshore Road, Fort Gratiot MI 48059, United States of America. Touch for directions.

Regionally, this marker is in Southeast Michigan

and in one of the Lake Huron Shore counties. It is also in the American Midwest.

Globally, it is in North America,

on the Great Lakes,

in the Western Hemisphere,

in the Western World,

and in the Anglosphere.

Historically, it finds itself in what was once the Northwest Territory.

Other nearby markers. At least 8 other markers are within 6 miles of this marker, measured as the crow flies: The 1971 Water Tunnel Explosion Memorial (here, next to this marker); What Lies Beneath (within shouting distance of this marker); Seeing the Light (approx. 5.7 miles away); The Storm (approx. 5.7 miles away); Learning from Lake Huron (approx. 5.7 miles away); Sending a Signal (approx. 5.7 miles away); Keepers Duties (approx. 5.7 miles away); Fort Gratiot Light (approx. 5.7 miles away). Touch for a list and map of all markers in Fort Gratiot.

Also see . . . 50th anniversary of Port Huron water tunnel explosion. Sarnia News Today website

Photographed by Joel S., September 19, 2015

3. Lake Huron Water Supply Project/Tunnel Explosion Marker

entry (Submitted on February 22, 2022, by Larry Gertner of New York, New York.)

Credits. This page was last revised on August 5, 2025. It was originally submitted on September 24, 2015, by Joel Seewald of Madison Heights, Michigan. This page has been viewed 1,827 times since then and 183 times this year. Photos: 1, 2, 3. submitted on September 24, 2015, by Joel Seewald of Madison Heights, Michigan.

Lake Huron Water Supply Project⎯⎯⎯Tunnel Explosion

Registered Michigan Historic Site

Lake Huron Water Supply Project
⎯⎯⎯
Tunnel Explosion