Jennifer has a number of photos of this Amphicar at “The Sand Bar” on Torch Lake (located in Antrim County).
I don’t know if it’s the same Amphicar that appears in these pictures (music warning), but it might be!
The History page at Amphicar.com says that:
The Amphicar was built in Germany from 1961 to 1968. Total production was 3,878 vehicles. The Amphicar is the only civilian amphibious passenger automobile ever to be mass produced. 3,046 Amphicars were imported into the United States between 1961 and 1967. The Amphicar is rear engined and uses a 4 cylinder British-built Triumph Herald motor producing 43hp. All Amphicars are convertibles, and the civilian models were originally offered in only 4 colors, Beach White, Regatta Red, Lagoon Blue and Fjord Green (Aqua).
The Amphicar has a top speed of 7mph on water and 70mph on land. Hence, it was dubbed the “Model 770”. The Amphicar is moved in the water by its twin nylon propellers … The “water transmission” is a 2-speed offering unique to the Amphicar featuring single forward and reverse gears. In the water, the front wheels act as rudders.
Be sure to click through for old photos (including on with the Mackinac Bridge in the background) and vintage ads and check amphicar.net for information about Amphicars in the Great Lakes region. I guess we better have a video of Amphicars in action too!