Siau hosts one of the most active volcanoes in Indonesia, thanks to the Karangetang volcano. The underwater topography reflects the towering cone above the island with many black porous rubbles scattered around.

The sensation of diving here, especially at night, is hearing the sound of the rumbling volcano. Also, the dramatic wall dive is covered in soft and hard corals, including Tubastrea corals and colonial anemones.

Different species of crustaceans, including lobsters and decorator crabs, are abundant here. Blue-spotted stingrays, cuttlefish, butterflyfish, angelfish, parrotfish, clownfish, and a school of barracudas, tunas, and mackerel are commonly spotted in the region.