In the 1960s, the American folk singer Pete Seeger devised an extraordinary plan: he built a 106-foot sailboat to save the polluted Hudson River. Down by the Riverside follows the unlikely story of the Clearwater, a boat that launched a movement. An intimate portrait of Pete, his wife Toshi, and the grassroots community they anchored for over 40 years, the film takes the audience on a musical and nautical odyssey, showing how an unconventional campaign to save a beloved American waterway prompted a green revolution. The tale of the Clearwater is a parable for our time, offering hope for a fractured nation and revealing how participatory imagination can solve environmental problems and transform how we relate not only to the earth but also to one another.