The Río Santo Domingo is a major tributary of the mighty Río Jataté, both essential arteries in eastern Chiapas  and the Lacandón rainforest, supporting numerous communities and ejidos along their banks. Centro Ecoturístico Causas Verdes Las Nubes (tel. 963/565-4710, ecoturismo_nubes [at] hotmail [dot] com, US$1 pp)—better known simply as Las Nubes (The Clouds)—is a popular water park located along a particularly turbulent stretch of the Río Santo Domingo.
The river, which grows to 50 meters across in some places, narrows considerably here as the water roars past in a series of stout waterfalls and churning rapids.
In the dry season the water is a striking turquoise hue similar to Agua Azul  near Ocosingo  (when it’s not a frothing white, that is). During heavy rain, sediment turns the water a turbid brown, but the added volume makes the rapids that much more dramatic.
Combi service to Las Nubes is provided by Transportador Tzobol (Comitán, 4a Av. Pte. Sur, near market, tel. 963/632-7739, US$3.75, 4 hrs) 8 a.m.–2 p.m. every day. Las Nubes is located 12 kilometers (7 miles) off of the Carretera Fronteriza ; the road is dirt but easily passable in a front-wheel-drive vehicle.