Beginning life some 450‑500 million years ago, the Earth's coral reefs are now the largest ecosystem upon the planet. They sustain and support over I million species worldwide and one coral reef alone may harbour some 3000 species. The major Indo‑Pacific ocean currents cross the seas that surround Sabah's sandy shores making them amongst the most biodiverse marine environments in the world. Within a single dive around Pulau Layang Layang divers may observe many of the 150 species of butterflyfish. Used by marine biologists as indicators of coral reef health, the greater the number and species diversity of butterflyfish reflects the abundance and diversity of corals. Pulau Layang Layang's pristine coral reef not only plays landlord to countless butterflyfish but also other reef dwellers such as, angelfish, snappers, wrasse, sweet lips, parrotfish as well as the larger pelagics; ‑barracuda, manta, schools of hammerhead sharks, dolphins and whales. Pulau Sipadan is famous for its vast numbers of Green and Hawksbill turtles which feed and breed within its waters before the females climb ashore to In their eggs above the white sandy beaches.

Diving on Sipadan's coral reefs the incredible phenomenon of the thousands of schooling chevron barracuda and big‑eye trevally or 'Jacks' can be witnessed. Floating inside such a tornado of fish is a truly breath‑taking experience that's very hard to beat. Sabah is also becoming a world famous location for muck diving'‑ the term used by divers to describe the search for the rare and exotic small marine animals. Many rare and newly identified gobies can be found living in the corals, sand, mud and mangroves of Sabah along with the little understood and rarely seen mimic octopus, neon patterned blue‑ringed octopus, delicate flamboyant cuttlefish, psychedelic mandarinfish and ghost pipefish. Sabah's dive guides are specifically trained to find such rarities and can show divers several of these oddities on a single dive.

Many new islands and reefs are being explored around the coast of Sabah and with this exploration comes the discovery of new dive sites and rarely seen marine creatures. Around north Sabah and the more recently discovered Mantanani Resort rare sightings of dugongs have been recorded. With the yearly occurance of whale sharks along the west coast during the months of December to February, Sabah really has some spectacular marine creatures to be discovered by the visiting divers.