Blackwater rivers, like the Suwannee River in Florida, carry waters so laden with organic material that they’re dyed a deep, dark brown. For the Suwannee, most of this material comes from the rich peat deposits of the Okefenokee Swamp that lies upstream. As vegetation in the swamp decays, tannins from the plants dissolve into the water, giving it its distinctive color, which the river maintains along its full 400-kilometer journey to the Gulf of Mexico. The dark waters of the river act as a tracer, revealing how the fresh river water mixes with the ocean in the enhanced-color satellite image above. It’s amazing to see how far the river’s influence spreads before delicate wisps of color pierce the darkness. (Image credit: U.S. Geological Survey; via NASA Earth Observatory)