By Sarah Burchell

Ira Gershenhorn swims where few would consider even dipping a toe, never mind submerging themselves.

As a local advocate for cleaner waterways, he plunges into the currents of the Hudson River off Manhattan’s Upper West Side not only for fun but to prove a point. Gerhsenhorn envisions a river free of pollutants and full of natural wildlife. As a researcher for the Billion Oyster Project, he regular samples its water for pollutants while maintaining colonies of filter-feeding oysters.

“If you bring the Hudson River and all the local rivers back to somewhere how they used to be, you can encourage all these animals to repopulate,” Gershenhorn said. “And they will!”