This image was posted by Chris Hadfield from the International Space Station on 20 April 2013 and captioned "St Lawrence's mouth, where the Great Lakes pour into the sea." See that circle on the right? That's what's really interesting.
It's a circular lake that's part of the Manicouagan impact crater.
This image of the crater was taken from the Space Shuttle in 1983.
The impact crater isn't obvious from the ground but from space it's quite clear. Pretty cool how things look different from up there.
Images via NASA