Residents fled mountains of “toxic foam” caused by an abnormal chemical reaction in a river.
Foam blew through the streets of a town called Mosquera, not far from the Colombian capital, Bogota.
The strange reaction was largely the result of detergent spilling into the nearby Balsillas River, local authorities said.
The river’s fast-moving waters, made more intense by recent heavy rains, also played a role, they added.
Putrid suds include surfactants and phosphates, which are also commonly found in household detergents and cause suds to form when mixed with water.
The end result is a foam rich in chemicals and pollutants.
Now residents have been told to be careful with detergents to prevent more toxic foam from forming.
Edwin Garcia, director of the Ambiental Environmental Laboratory, said: “It is important to state that one of the main generators of this foam are detergents.
“This is why the community and businesses are asked to make very rational use of these products, which cause foam formation.
“Contact with turbulent water and heavy rainfall generate this phenomenon in the water.”
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This has in fact been an ongoing problem for residents of Mosquera despite the authorities building a sewage treatment plant two years ago.
Residents are extremely concerned about moss, not only in terms of their own health, but also the ripple effect it has on their town and its businesses.
Local store owner Luis Eduardo Romero said: “Health is the issue.
“The moss affects everything, for example the moss falls on the doors and everything rots.
“How [bad] would it be with the food we sell here.”
Images from Mosquera show the walls of shops and houses covered in acrid white moss.
Many people have been seen in dramatic footage trying to sweep the moss from inside their homes.
Others were forced to completely abandon their residence.