I think you just gave about fifty enviromentalists heart attacks.
Maybe there's some other non-toxic liquid that floats that could do the same thing. Can't think of one, offhand.
And then, of course, as soon as you get waves and breakers you're pretty much screwed.
Maybe drop about fifty trillion ice cubes into the Gulf? A monstrous solar shade in orbit that blocks the sun from the Gulf? Call for Superman?
