The High Island Reservoir, located in the Sai Kung Country Park, is the largest reservoir in Hong Kong. The construction work was magnificent, which entailed the building of two rock dams rising 64 metres above mean sea level at the eastern and western approaches of the narrow strait running between High Island and the eastern end of the Sai Kung Peninsula to form a reservoir with a capacity of 280 million cubic metres. Work began in 1971 and was completed in 1979.

The east main cofferdam of High Island Reservoir protected by the concrete "Dolosse" is unique and distinctive. Standing on the dam to enjoy the moist sea breeze while admiring the sight of sunrise is certainly an extraordinary thing to do. The surrounding of east main dam and Po Pin Chau by the queer looking hexagonal tuff is also a grandeur.