“Riptide,” the image you’re talking about, is actually where the water goes out, about eighty miles beyond the Mississippi, where the water streams into the Gulf of Mexico. It’s silted, so there’s a certain opaque tonality to the Mississippi water. The Gulf of Mexico is a clearer, and has an aquamarine-blue appearance. It’s where brackish water meets the salty ocean water of the Gulf. That particular intersection in the photograph is where these two different types of water are actually coalescing and blending together. The oil had found its path into that water too, so it was caught into the confluence of these two waters. The oil is being held in that tide, and that is one of the few places where I was actually able to see the oil.
-Edward Burtynsky (cool interview on APE, click through!)