The brown tint of the water is mostly from river runoff. If you look at satelite photos of the Mississippi River delta
, you can actually see the swirling brown silt flowing into the gulf. The water does get clearer as you go farther out though. How far do you have to go to find "clear" water, I really don't know. I for one enjoy an open water swim call from time to time but there is always this self preservation part of my brain that believes that every fish and shark in the oceans are swimming right below my feet.