The Waterkeeper Alliance supports a relatively new but fast-growing professional corps. At their annual conference in Wilmington, North Carolina, in June, there were more than 200 riverkeepers, baykeepers, coastkeepers—even a Himalayan glacierkeeper. Collectively, the keepers patrol millions of square miles of waterways, inland and along the coast, defending watersheds that billions of people rely on for drinking, bathing, and food production. The keeper mission is stated on the T-shirts many of them wear: “We hold polluters accountable.” Members of the alliance can be individuals, or they can be bustling organizations that employ lawyers, scientists, educators, and community organizers. Hudson Riverkeeper—the first keeper organization—now has a full-time staff of more than two-dozen people.

At the helm of the Waterkeeper Alliance is its founder, Robert F. Kennedy Jr., who now serves as its president and senior attorney. Kennedy’s early work with Hudson Riverkeeper set lasting standards for environmental law and inspired the creation of hundreds of similar organizations throughout the United States and abroad, helping to fuel the keeper movement. With Hudson Riverkeeper and the N.R.D.C., he won historic victories against massive corporate polluters such as Con Edison and General Electric, forcing the former to abandon development plans that would have destroyed critical spawning grounds and the latter to contribute to cleanup efforts for P.C.B.s and other poisons dumped in the river. He also led negotiations on a crucial watershed agreement providing reservoirs for New York City’s drinking water, now regarded as an international model in sustainable development.

Kennedy maintains a busy schedule. He is also a professor of environmental law at Pace University’s law school and co-director of the Pace Environmental Litigation Clinic, which offers legal support to keeper organizations. He co-hosts a radio show (Ring of Fire on Air America Radio) and has written numerous magazine articles as well as several books, including The Riverkeepers (1999) and the New York Times best-seller Crimes Against Nature (2004). Kennedy has two new books forthcoming (on public health and on U.S. foreign policy under the Kennedys) and one released last month (on his cousin Michael Skakel). When he’s not working he spends much of his time outdoors, often with his six children (now mostly grown). He is a licensed master falconer, and a veteran of white-water paddling trips, having led the first descents on three little-known rivers in Peru, Colombia, and Venezuela.

This year’s conference marked the 50th anniversary of the keeper movement, and Kennedy delivered his keynote address to the largest group of keepers ever. Many in the assembled crowd clamored for a view of Kennedy’s tattoo (an Atlantic sturgeon, the official logo of the Waterkeeper Alliance). Nearly 100 of the keepers have similar tattoos, either as a sign of their commitment to the cause, or perhaps just because they’re a venturesome bunch. Kennedy, in his venturesome way, spoke to Vanity Fair about the keeper movement and where it’s headed.

Vanity Fair: In 2008 you wrote an article in Vanity Fair urging the next president to promote clean-energy markets and innovation. How do you think President Obama has done on that front, and on environmental stewardship in general?

Robert F. Kennedy Jr.: I think he’s been a good environmental president. In comparison to his predecessors, he’s done an extraordinary job. In comparison to what I’d like him to do, it’s been less extraordinary, but I think we should put the United States on a war footing; we ought to take the same steps that we did during World War II and say this is the biggest challenge that humanity faces, the biggest threat to our security and our nation, and we need to convert off coal and oil and do it within a decade. And I think a president could do that. That’s not what he did, but, you know, he did make tremendous changes. One of [the] most dramatic things he did very early in his presidency was to get higher fuel-economy standards, which have dramatically changed the profile of how we use fuel energy in this country for transportation fuel.