The activity for which Bonito is most famous is flutuação, which consists of donning a mask, snorkel, neoprene wetsuit, and life jacket and letting yourself be carried down Bonito’s rivers, whose unearthly transparency allows you astonishing close-up interaction with over 80 varieties of fish. The sensation is akin to being let loose within a giant tropical aquarium (for this reason don’t show up without an underwater camera). The fantastic visibility (which extends to 50 meters/164 feet) is due to the water’s high limestone content, which acts as a natural filter, leaving the rivers exceptionally pure.

You don’t need to have any diving experience to “float”: After a few practice sessions with monitors, just let yourself quite literally go with the flow. Among the colorful fish you’ll find yourself rubbing up against are piraputangas, dourados, and curimbatás—rest assured that piranhas prefer other aquatic pastures.

One of Bonito’s most popular attractions, the Aquário Natural (7 km/4 miles from Bonito) is a wildlife sanctuary whose crystalline rivers can be explored with snorkeling equipment or glass-bottomed boats. Recommended for beginners (there is a training session before you hit the river itself), this 0.5-kilometer (0.3-mile) underwater excursion is dazzling, but all-too-brief—its popularity limits your floating time to one hour. The price, R$125, includes lunch and access to hiking trails.

Longer and equally stunning (not to mention less expensive) floating experiences can be had on the Rio Formoso (Rodovia Guia Lopes, 6 km/3.5 miles from Bonito), Rio Baía Bonita (BR-267 to Jardim, 7 km/4 miles from Bonito), the Rio Sucuri (Estrada São Geraldo, 17 km/10.5 miles from Bonito), and Rio da Prata (BR-267 Km 518, 50 km/31 miles from Bonito). Rio Sucuri is particularly spectacular. The excursion begins at the river’s source and then continues for 1.5 kilometers (0.9 mile) along a river bed that is lined with a swaying jungle of aquatic plants. Equipment rental and guides are available at all the fazendas through which these rivers flow.

Equally fantastic is Rio da Prata—the clear waters are always teeming with fish, and the 2-kilometer (1.2-mile) route itself (preceded by a 40-minute hike through the forest) is Bonito’s longest.

It is also possible to go scuba diving in the Rio Formoso, Rio da Prata, and the Abismo Anhumas. Bonito Scuba (Rua Colonel Pilad Rebuá 1853, tel. 67/3255-2040, www.bonitoscuba.com.br) organizes diving trips and offers lessons.