When Arun Krishnamurthy was a child in the 1990s, his middle-class suburb in Chennai, India, was only half built. He didn’t have to wander far from his house to find green fields and lakes, where he would spend hours alone watching frogs and dodging snakes.

Krishnamurthy, now 36, was lucky. Since 2000, India’s population has grown by nearly a third, and its economy has more than quintupled. Those booms have put immense pressure on the country’s natural areas, he says.

Krishnamurthy started trying to correct that at 20. He organized a group of friends and neighbors to clean up a polluted pond in Chennai, where it snowballed.

Environmentalist Arun Krishnamurthy is one of TIME Magazine's 2022 Next Generation Leaders.