Isla San Pedro Nolasco is a protected marine reserve about 30 kilometres from San Carlos, accessible by boat trip arranged through the dive operators in the San Carlos marinas. The island itself is a rocky volcanic outcrop with no permanent habitation, but its surrounding waters are among the most productive dive sites in the Sea of Cortez — sea lion colonies that interact with divers, large schools of fish around the underwater walls, and the occasional whale shark.
The trip from San Carlos takes about 45 minutes in a fast panga; most operators offer snorkelling as well as scuba. The island's sea lion colony is the main draw, but the dive wall on the island's lee side — dropping to around 30 metres with visibility often exceeding 20 metres — is one of the better dive sites in northwest Mexico.