Southern Chile's Class II Río Baker may appear condemned by a government plan to build four major dams, but there's hope yet—and you can play a role. Start by joining Patagonia Adventure Expeditions' meandering eight-day, 100-mile Río Baker float through Patagonia's remote Aysén region ($1,350; adventurepatagonia.com). Then donate to the NRDC (savebiogems.org), the American voice in the fight.