India, April 5 -- She was 35 when she first set eyes on the Pallikarani Marsh.

About 20 km from the centre of Chennai, the wetland wasn't much to look at. Construction debris and garbage had been dumped here; sewage was being released into the area untreated. Large parts had been encroached upon.

"At the time, the marshes didn't even have a name," says Jayshree Vencatesan, 59. The area was referred to as "kazhuveli", Tamil for "a place that drains". This was a traditional form of land classification, even in government documents.

Vencatesan, who had just completed a PhD at the MS Swaminathan Research Foundation, knew the marshes were more than that. She had just received a grant of Rs.32,000 from the Tamil Nadu Pollution Control Board,...