Back along the Río Dulce, another kilometer or so upstream, is a spot where warm sulfurous waters bubble from the base of a cliff, providing a pleasant place to swim. Shortly thereafter, the river widens into a lake known as El Golfete.

The lake is home to a dwindling population of manatees protected on its northern shore by the Chocón Machacas Biotope (7 a.m.–4 p.m. daily, $5). The large, slow-moving aquatic mammals (also known as sea cows) are extremely elusive creatures and fewer than 100 are thought to inhabit these waters. The walruslike animals are threatened throughout their range by long reproductive cycles (they reach sexual maturity late in life) and collisions with motorboats.

The 186-square-kilometer (72-square-mile) park is run by CECON and there are aquatic routes through several jungle lagoons as well as a nature trail running through the park and its protected forests.

The river continues its course upstream past the expensive villas of Guatemala’s oligarchy to the town of Río Dulce, at the confluence of the river and Lake Izabal. A long bridge connects both shores along Highway CA-13, which continues north to Petén.