The waters around Guaymas and San Carlos offer some of the best diving in the Americas: hammerhead sharks schooling at depth, whale sharks that pass through in summer, colonies of sea lions on the offshore rocks, manta rays, enormous schools of fish, and a seafloor covered in brilliant corals and sponges. Jacques Cousteau filmed here and called the Sea of Cortez "the aquarium of the world" — a reputation the waters still deserve.
Several dive operators in San Carlos offer day trips to the best sites. Pedro Nolasco Island, about 30 km north, is the premier location — a protected marine park with sea lion colonies, Panamic green moray eels, and walls of marine life that reward both snorkellers and divers. The best conditions are from August through the cooler winter months; summer is hot above water but productive below it.