Koh Bida Nok is one of the best dive sites in Koh Phi Phi. The northern part drops to 35 meters (115 feet) and offers great wall diving and also a few caverns. The walls are covered with soft corals, sea fans, anemones, barrel sponges, and whip corals. Moving south, the reef becomes shallower, finishing in a small lagoon at the southern part.
Marine life includes sea turtles, giant moray eels, schools of snappers, hunting jacks,nudibranchs, barracudas, lionfish, sweetlips, and sea snakes. On the west wall of the islet, divers can sometimes spot nurse sharks and bamboo sharks. Although not common, whale sharks and manta rays may also make an appearance from December to February. In the shallow lagoon, juvenile blacktip sharks can be found near the seabed.
The best time to dive Koh Bida Nok is February through May. The water temperature ranges from 27° to 30° C (80-86° F).