The smog-clad Yamuna river in Delhi is polluted with toxic foam floating over its surface, drone footage shot on Tuesday, 21 November shows.Foam covered the water amid the Indian capital’s annual battle on pollution, which gets worse in winter when wind speeds drop and cooling air traps pollutants emitted by vehicles, industry, and farmers burning agricultural waste.Sludge and untreated waste are responsible for the foam, a former adviser to the Delhi government said.They added that the city's water board was spraying a food-grade chemical to bring it under control.Source: Reuters, ANI