The miracle of Kolkata's wetlands – and one man's struggle to save them

The wetlands are this Indian city's free sewage works, a fertile aquatic garden and, most importantly, a flood defence - but they're under threat from developers. One environmentalist is leading the resistance

The trees on the streets of Kolkata in January are dusty, like neglected pot plants. At traffic lights, salesmen offer feather dusters for drivers to wipe their grimy cars. Shrubs are planted on the central reservation of the city's new flyovers, surrounded by the implausible boasts on signs proclaiming a "clean and green" city. But the most frequently recurring poster, above almost every street corner, appeals for investors to "Come to Bengal - Ride the Growth".

Kolkata, a famously cultured city of 14.5 million people - once the second city of the British empire after London - is keen to catch up with Delhi, Mumbai, Chennai and Bangalore, the dynamic and rapidly modernising megacities of the fastest growing major economy in the world.