As the worshippers descended the slope to the riverbank, dressed in their festival best and carrying offerings, a voice on the loudspeaker repeated: "The water is deep, don’t let go of your child’s hand, don’t let them in the water.”

It was a much-needed warning for the thousands of families in attendance for the four-day Hindu festival of Chhath that ended Thursday, a celebration of the sun deity Surya that involves fasting and making offerings while standing in water.

They needed the warning because the river’s water was, in fact, barely visible, blanketed with a toxic foam of industrial waste and sewage. If you didn’t know better, you could mistake it for the morning after a night of heavy snowfall.