Dean Naujoks fires up the engine of his boat at the Bell Haven Marina in Alexandria, Virginia, and heads out to his version of an office cubicle: the wide, windy, greenish-gray currents of the Potomac River.“This is the Woodrow Wilson Bridge,” Naujoks says as he guides the boat on a sunny morning. “And then right over here is Jones Point Lighthouse. This is the oldest riverine lighthouse in the country.”For the last three and a half years, Naujoks – a 49-year-old veteran environmental activist and son of a tool-and-die maker from Eastern Pennsylvania – has worked as the Potomac Riverkeeper, leading a nonprofit organization that advocates for cleaner water.