Sangalaki is known for the large gatherings of manta rays that come here to feed on plankton. Most dives here are in shallow water, since the mantas feed near the surface.
Visibility is somewhat restricted, specially during the rainy season (November to March). Sangalaki does not have walls like Sipadan, it is surrounded by a shallow lagoon and the reefs start a distance out from the island, dropping from about 4m to 18 to 24m and up to 40m at some point.
The island itself is a breeding ground for green turtles. At night female turtles come ashore and lay their eggs and small baby turtles can be seen regularly, when they hatch.
The island and its surrounding reefs are protected as an Indonesian Marine Park.