India, July 21 -- Delhi's toxic relationship with the Yamuna is well established now, with the past decade defined by toxic foam, foul stench and unending pollution. While the stretch from Wazirabad to Okhla is routinely choked with raw sewage, plastic waste and industrial effluents-which manifest as foam downstream-a 21-kilometre stretch between Palla and Wazirabad, which was considered clean, seems to be succumbing to the Yamuna toxification.

Delhi draws its drinking water from Wazirabad, before the bulk of drains empty into the Yamuna just ahead of this stretch, defined by floodplains that host fields of marigold, strawberry and other seasonal produce, perpetuating a belief that this was Delhi's last breath of fresh water.

However, w...