Most of the natural river water is clear, but if there are more algae in the water, the river looks green. Water looks blue when containing more calcium carbonate, looks red with more sulfur, and looks black with more mud. Industrial pollution also changes the river colors. For example, effluent containing high amount of copper shows blue, and the wastewater from the paper factory looks black. The source of these colors are the chemicals, which adds colors to the riverbanks, rocks and embankment.