El Yunque National Forest receives 240 inches of rainfall annually, more than any other forest in the U.S. system, feeding 16 named waterfalls and hundreds of unnamed cascades across 28,000 acres of montane terrain. Designated a forest reserve in 1876 under Spanish colonial rule, El Yunque became part of the U.S. National Forest System in 1903, making it the oldest reserve in the Western Hemisphere and the only tropical rainforest under American jurisdiction. The Taíno people called it Yuké, home of their benevolent god, and considered its peaks sacred long before European contact. The forest rises from sea level to 3,533 feet at El Toro peak, creating four distinct life zones: tabonuco rainforest below 2,000 feet, palo colorado cloud forest between 2,000 and 3,000 feet, dwarf forest above 3,000 feet, and palm forest along streams. This vertical stratification supports 225 tree species, 23 of which exist nowhere else on Earth. The Puerto Rican parrot, critically endangered with fewer than 600 individuals remaining in 2026, nests exclusively in El Yunque's sierra palm groves. Hurricane Maria in 2017 stripped 95 percent of the forest's canopy, but regeneration has been faster than predicted, with understory ferns and heliconia now thriving in sunlit gaps. Most Puerto Rico rainforest waterfall tour itineraries concentrate on the Río Mameyes and Río Sabana watersheds, where accessible trails lead to swimming holes carved into andesite bedrock. La Mina Falls, the most visited cascade, drops 35 feet into a stone basin reached by a paved 0.7-mile trail from the Palo Colorado Information Center. Less crowded alternatives include Juan Diego Creek, where natural rock slides funnel swimmers into deep pools, and the upper Mameyes tributaries, which require river crossings and hand-over-hand scrambles. Water temperature holds steady at 70 degrees year-round, fed by high-elevation springs. El Yunque's waterfall geography reflects its volcanic origins. The forest sits atop the Sierra de Luquillo, a fault-block massif pushed upward during the Cretaceous period when the Caribbean and North American plates collided. Rapid erosion along fracture lines created the steep-walled valleys and vertical drops that define the watershed today. Trade winds from the northeast slam moisture-laden air into the mountain face, forcing orographic lift and near-constant precipitation above 1,500 feet. This hydrological engine has run uninterrupted for millennia, sculpting stone into flumes and basins that now anchor the island's ecotourism economy.