Isla San Pedro Nolasco lies about 27 kilometres west of San Carlos and is one of the best diving destinations in the northern Sea of Cortez. The island is uninhabited and protected as a natural reserve, which means the marine life is unusually dense and unafraid. Day trips run from the San Carlos marina, with the crossing taking roughly 45 minutes by panga.
The dive sites range from shallow rocky reefs ideal for snorkelling to deep walls and an underwater arch at South Point. The permanent residents include a large colony of California sea lions, hawksbill sea turtles, moray eels, and a wide variety of reef fish. Bottlenose dolphins frequently join the boat on the crossing. Visibility is typically 15 to 20 metres and the water temperature stays warm enough for a 3mm wetsuit for most of the year, though a 5mm is more comfortable in winter.