The dam's dolosse units each weigh 25 tons to withstand the extreme hydraulic force of typhoon-driven waves.
The hexagonal rock columns were formed through the rapid cooling of thick rhyolitic ash flows in a supervolcano caldera.
High Island was an actual island until the reservoir construction project linked it to the mainland via two massive rock dams in the 1970s.
The reservoir has a total capacity of approximately 273 million cubic meters of water.
The rock columns here are among the largest and most well-preserved examples of hexagonal volcanic joints in the world.
Visible dykes cutting through the volcanic tuff illustrate the history of magma intrusions into the surrounding rock layers.
High Island Reservoir East Dam is the largest reservoir in Hong Kong, located within the Hong Kong UNESCO Global Geopark. The site is characterized by massive S-shaped dolosse concrete blocks designed to dissipate wave energy and protect the dam from the South China Sea. Visitors can observe distinct hexagonal volcanic tuff columns formed approximately 140 million years ago during the Mesozoic era. These rhyolitic volcanic rocks are part of the Geopark’s Sai Kung Volcanic Rock Region. The dam connects the main reservoir structure to the rugged coastline of the High Island peninsula. Geological features include fault lines and dykes visible within the cliff faces near the reservoir. The site serves as a vital component of Hong Kong's water supply infrastructure, constructed by damming a channel between High Island and the Sai Kung Peninsula. The area remains an exposed environment with limited natural shade.
The view from the top of the dam looking down at the pattern of the S-shaped dolosse blocks.
Bring high-factor sun protection as there is minimal tree cover on the dam or the coastal trail.
Carry sufficient water as there are no shops or vending machines once you reach the dam area.
Check the local weather forecast specifically for the Sai Kung area, as wind speeds on the dam are significantly higher than in the city.
Do not attempt to swim in the reservoir or the adjacent sea, as both are hazardous and prohibited.
Access may be restricted during extreme weather conditions such as typhoon warnings.
Do not climb on the wave-dissipating concrete blocks; maintain distance from the cliff edges due to loose rock risks.
