The Great Blue Hole is a cave site in the Caribbean Sea off Belize. It reaches a depth of 124 metres and is rated for advanced divers. It lies within a Natural Monument that forms part of the Belize Barrier Reef Reserve System World Heritage Site. Fishing, spearfishing and any take or collection of marine life are prohibited; only diving and snorkelling are permitted. Jacques Cousteau called it one of the top five scuba diving sites in the world. The best months to dive are December to April. Caribbean reef sharks, nurse sharks, crustaceans and big reef fish are resident. Giant grouper and scalloped hammerhead sharks are occasionally seen.