Pui O is a bay shaped by the Chi Ma Wan Peninsula and the lower slopes of Sunset Peak. A main river from a valley to the east and other small river gather at Pui O forming an estuary of wetland. Villagers enclosed the wetland and converted it into rice paddies. This is indicated by the name Ham Tin (). At the shore, a long beach (or spit) is formed by the interaction between the current of the South China Sea and the rivers.