Actually the first Mayor Daley was pushing a plan in the 60s for an artificial island in Lake Michigan for a third major Chicago airport. Here is an item from a blog that I recently found that tells the story.

Mayor Richard J. Daley, the current mayor's late father, tried to get such a scheme going several times in the 1960s. It never took off (ha ha) for a number of reasons. Chief among them is that building in Lake Michigan is like building in the North Atlantic, and a structure large enough to hold an airport would have been incredibly expensive. But even before eco-awareness hit there was a lot of resistance to the idea of destroying one of Chicago's primary assets, the view of Lake Michigan, with a manmade structure. Once the EPA came into being and environmental impact statements were required there was no way such a project would ever occur.
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