Less than a mile from Manhattan in the middle of the East River is North Brother Island, the former home of a notorious typhoid hospital. Today the hospital lies in ruins, and nature is taking over.

New York’s Bronx River—once an open sewer—is now teeming with life. We discovered oysters, eels, herons, and even beavers, as we canoed through the poorest congressional district in America.

We know that green roofs cool our buildings and absorb storm water. But could they also provide habitat for wildlife? To find out, we got special access to five private rooftops in New York and Chicago.

If you take the ‘A’ train to the end of the line in Queens, you land at Jamaica Bay, where salt marshes support endangered birds and rare turtles. We patrolled these waters with an activist known as the Jamaica Bay Guardian.

It’s a seemingly impossible task: cataloguing every wild plant species in Central Park. But that’s exactly what two botanists are doing, and they’re making some surprising discoveries along the way.