A layer of toxic foam has spilled over from a contaminated river into the Colombian city of Mosquera, often breaking into cloudlike chunks that drift with the wind along streets and into yards.

Key points:

• The fetid foam is plaguing the city of Mosquera, 20 kilometres north-west of the Colombian capital, Bogota
• Environmental authorities blame discharge from an industrial zone, combining with household detergents, for the foam
• This foam forms when a narrowing of the river, or a bridge, creates turbulence in contaminated water

Environmental authorities blame discharge from an industrial zone, as well as household detergents, which — when combined — whip up the fetid foam that is blown into the city some 20 kilometres outside Bogota, Colombia's capital.

Gonzalo Roa — who has lived in the Los Puentes neighbourhood for 40 years — blamed the contamination for causing respiratory problems in children.

"We've had many years of this situation," he said.

The foam is usually created when a narrowing of the river or a bridge creates turbulence in the contaminated water, according to Luis Alejandro Camacho Botero, an expert on environmental hydraulics at the University of the Andes.

He said similar problems existed along other rivers, including the Bogota River, and warned the foam will bring public health problems if not controlled.

Edwin García — the director of the environmental laboratory for the Cundinamarca region — said authorities were trying to monitor and reduce the problem and have installed a water-treatment plant.