In Mosquera, Colombia, pollution in the local river has gotten so bad that toxic foam has begun to form in building-sized piles. The putrid foam forms when poorly treated or untreated sewage spills into the water. Surfactants and phosphates present in the pollution, which are also commonly found in household detergents, then cause foaming when mixed with water.
The end result is a foam ripe with chemicals and pollutants that are both damaging to the environment and anyone exposed. This foaming phenomenon occurs in other parts of the world where pollution levels are high, such as in India's Yamuna River.