Renggis Island is one of Tioman's top dive spots, hence it can get busy at times. Sub surface on the eastern side of the island is a reef teeming with life with all manner of corals, sponges and anemones and a multitude of fish. This site is often used for training and night dives, it is also one of the better places to spot turtles and blacktip sharks.
The western side of the island has a lot of Gorgonians and is home to several turtles and a resident giant barracuda called Boris. Venturing off the island reefs and into slightly deeper water will reveal a couple of Thai fishing wrecks that house a moray eel. There is also another "hidden reef" out here with equally as impressive corals and fish life.