Weizhou Island's coral reefs are the healthiest remaining in the northern South China Sea, protected by the island's relative isolation from industrial development on the Guangxi coast. The warm water of the Gulf of Tonkin (sea temperature 24–28°C from April through November) supports hard coral formations accessible from shore at several points around the island's southern and eastern coasts. Green sea turtles nest on the beaches in summer and are visible in the water year-round.
Snorkelling is possible directly from the beach at several spots without a boat or tour. The marine reserve status restricts fishing in the core areas, which has allowed reef fish populations to recover in the past decade. If you want to dive rather than snorkel, there are basic dive operations in the main village that rent equipment and offer guided dives for certified divers. The visibility is best in October and November when the plankton blooms ease. Come in summer if you want the warmest water; come in autumn if you want to see the most.