This image shows water quality changes in the Gulf of Mexico. Reds and oranges represent high concentrations of algae and river sediment. Under certain conditions excessive algal growth can result in a "dead zone" of low oxygen.
Credit (via NASA/Goddard Conceptual Image Lab)
An illustration of the flow of water from tributaries in the middle of the United States, down the Mississippi River, and into the Gulf of Mexico. Pollutants impacting the health of the River and Gulf can originate far inland.