It's quite possible you've never seen a marine railway - though the concept is nearly two hundred years old, they're not exactly ubiquitous. Marine railways enable maritime traffic to go between two separate bodies of water through the use of a cradle that carries them out of one body of water and into the other. When I was growing up, the closest was the Big Chute Marine Railway in Muskoka, which has incidentally been instrumental in preventing the spread of zebra mussels.
This photo is a framegrab from a camcorder video that was taken on July 28, 1991.
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