The Yamuna River, India's most polluted river, stretches 1,375km (855 miles) across the northern part of the country. Along the way, the river goes through a dramatic transformation – from crystal clear near its Himalayan source to some of the world's most contaminated waters as it passes through the capital New Delhi. Yamuna is also home to a resilient community of slum divers, who brave even the bone-chilling cold of winter to dive into the river and retrieve coins from its depths. The coins are offerings made to the river goddess by passengers on boats crossing the river. This is the story of Sanjay, a senior diver who not only takes great pride in his work, but is also something of a local hero after rescuing many people from drowning.