It's no surprise that RFK Jr. cares passionately about water—he's been sailing, fishing, and paddling since childhood. But what he's accomplished with that passion is astonishing. Simply put, the iconic Kennedy—master falconer, avid kayaker, and son of the late senator Robert F. Kennedy—is one of the leading environmental advocates of our time. He's the chief prosecuting attorney for Riverkeeper, a nonprofit group devoted to protecting New York's Hudson River watershed, and president of Waterkeeper Alliance, an international network of water defenders. He's also the senior attorney for the Natural Resources Defense Council and co-author—with acclaimed New York water warrior John Cronin—of The Riverkeepers. Along the way, Kennedy, 53, has helped command one of America's brightest eco-successes: the cleanup of the Hudson, whose now swimmable waters were once largely a liquid garbage bin. But his most recent book, Crimes Against Nature—a takedown of the Bush administration's environmental record—perhaps best highlights his core belief: that our obligation to nature is a moral one, the shunning of which harms not only the future but the very fabric of society. Senior editor AMY LINN spoke with him about his crusade.

OUTSIDE: What made water issues such a calling?
KENNEDY: I spent most of my early life wandering the creeks around my home in Virginia and spending summers on the Cape, fishing almost every day. On vacations my father would take us to the whitewater rivers. We ran the Salmon, the Snake, and the Colorado, the Yampa, the Green, and the upper Hudson. And I always understood that water wasn't just an environmental issue; it was a civil-rights issue—a human-rights issue. The best way of measuring the success of a democracy is how it distributes the goods of the land—the commons.

Did you see threats long ago?
I couldn't swim in the Hudson or the Charles or the Potomac when I was growing up. I was shocked, when I ran the upper Hudson, when the guides told us it was poisonous to drink. And I always recognized that as an act of theft—that pollution was a theft. It was the act of a big shot with political clout stealing from the rest of us—stealing publicly owned resources from the public.

What's at stake?
The relationship with nature is so critical to our culture. We're not protecting nature for the sake of fishes and birds. We're protecting nature for our culture, for our prosperity, for our quality of life.

And if we want to meet our obligation as a generation, as a nation, as a civilization—which is to create communities for our children that provide them with the same opportunities for dignity and enrichment and good health as the communities that our parents gave us—then we've got to start by protecting our environmental infrastructure. We've got to protect the air we breathe, the water we drink, the wildlife, the public lands, the waterways that enrich us, that connect us to our past, that provide context to our communities—and that are the source, ultimately, of our values and virtues and character as a people.

How does a Waterkeeper help?
Every Waterkeeper has a patrol boat on the water. We also take the public out, and take journalists out. We do this to constantly remind the public that this is their property. The polluters want to make the public think the waterways belong to them—that they're just a waste conveyance.

Is there a way to bring the message close to home?
If General Electric pulled a truck up to your lawn and dumped PCBs into your yard, you would fight them until they removed the last molecule. So why don't we react the same way when they dump PCBs into our river?

What's the most important thing people can do?
They have to be willing to fight—that's all. You have to be willing to fight.

For more on water, visit waterkeeper.org or nrdc.org.