The color appearance of a body of water is also STRONGLY affected by the earth at the bottom and sides (if any) of that body of water.
For example, I live by Atlantic City, NJ. Our ocean water quality is EXCELLENT, it's tested daily during the summer. The water is as clean as clean can be. But most of the time when you look at the ocean it appears to be a dark green or dark grey with a dark-bluish tinge. But if you put the water in a bucket or a glass, it's crystal clear.
I'll never forget my first trip to the Caribbean (the REAL Caribbean, not CBR) and how bright BLUE the water was. My wife and I just assumed the water was cleaner there. Then people there explained to us that it's a matter of the color and reflective/refractive properties of the sand. The sand in that part of the world bends the light in a certain way after it bounces of the bottom, rather than absorbing the light like the sand in most of the eastern USA. I tried this out, and when you put it in a clear glass, the water in the beautiful blue Caribbean Sea is the same colorless crystal clear as our water here at the South Jersey shore.
On the Sassagoula, don't forget that it's probably pretty shallow (and very definitely man-made), so the boat's propellors churn up the water and disturb the sediment on the bottom.
I really disagree that oil and/or fuel from the boats on the Sassagoula contributes to a brownish color of the water. Oil and fuel would float on top, not be mixed in, and would appear as a translucent, rainbow-colored sheen on the water's surface.