Bluff Island, indigneously known as Sha Tong Hau Shan (Chinese: 沙塘口山), also known as Ung Kong (甕缸), is an island in Port Shelter, south of Sai Kung Peninsula of Hong Kong. It is an important area for corals and other marine life. The island is zoned as Site of Special Scientific Interest in 1979. The surrounding water has not yet been legally protected and thus the corals are damaged by anchors of holiday visitors.
An open U-shaped bay, Ung Kong Wan (甕缸灣), is located at the north of the island.