History & Context
High Island takes its name from Ha Kwu Chau, a former island that once sat in open water between the Sai Kung Peninsula and a scatter of smaller islets in Port Shelter. Facing an acute freshwater shortage through the mid-20th century — a constraint severe enough that Hong Kong periodically relied on scheduled mainland water rationing and imported supply from Guangdong — the colonial government undertook one of its most ambitious civil engineering projects to close off both the eastern and western channels around the island with rockfill dams, converting the enclosed sea channel into a freshwater reservoir. Construction ran through the 1970s and the reservoir began impounding water before the East Dam’s completion in 1978, sealing what had been open coastal water into what remains the largest water storage facility in Hong Kong by capacity, holding up to roughly 273 million cubic meters. The engineering effectively erased High Island as a discrete island, fusing its former landmass into the Sai Kung Peninsula’s coastline. The surrounding terrain now falls within Sai Kung East Country Park, one of the country parks designated in 1978 as part of a wider mid-1970s push to protect the New Territories’ undeveloped hill and coastal land from the city’s rapid postwar expansion.
Before the dams were built, the channel between Ha Kwu Chau and the mainland peninsula was itself a fishing ground and a passage used by small craft moving between Sai Kung and the sheltered bays further east; older residents of Sai Kung town still recall the area’s pre-reservoir geography, though the physical evidence of that older coastline is now submerged beneath the impounded freshwater or buried under the dam’s rockfill embankments.
Geology & Landscape
The defining feature of this protected coastal zone is an extensive exposure of light-coloured, silica-rich rhyolitic volcanic rock, formed as thick volcanic ash and lava cooled and contracted following a series of eruptions roughly 140 million years ago. As the molten rock cooled from the outside in, it fractured into the tall, roughly hexagonal columns now exposed along the East Dam cliffs — a geological process similar to the one that produced Northern Ireland’s Giant’s Causeway and Iceland’s basalt columns, though the High Island columns are unusual in being composed of rhyolite rather than the darker basalt typical of most columnar joint formations elsewhere in the world. The formation was recognized as one of the International Union of Geological Sciences’ first 100 Geological Heritage Sites and sits at the heart of the Hong Kong UNESCO Global Geopark, whose broader volcanic rock region is described as the largest continuous exposure of hexagonal columns anywhere on the planet. Visitors traversing the East Dam can observe fault lines, sea caves, and wave-cut platforms shaped by continual marine erosion from the South China Sea, alongside the dam’s own engineered breakwater structure, built from tetrapod-shaped concrete armor units designed to dissipate wave energy before it reaches the rockfill core.
Economic Context & Water Security
High Island Reservoir remains a working part of the Water Supplies Department’s freshwater infrastructure rather than a purely scenic site, and its construction marked a turning point in Hong Kong’s long effort to reduce dependence on rainfall variability and imported mainland water. Alongside the Dongjiang (East River) water supply agreement with Guangdong, reservoirs of this scale allowed Hong Kong to move away from the intermittent water rationing that had periodically disrupted daily life for residents through the 1960s. The reservoir’s dual role — critical municipal infrastructure and a globally significant geological site sitting on top of it — is unusual even by Hong Kong’s standards of layering utility over landscape.
Conservation & Visitor Management
The same geological rarity that makes High Island a draw for hikers and photographers also makes it fragile in ways less obvious than a beach or a forest trail. The exposed rock columns are a finite, non-renewable geological record, and the Hong Kong UNESCO Global Geopark’s management framework — jointly overseen with the Country and Marine Parks authorities — restricts activities such as rock climbing, drone flying in certain zones, and the removal of any rock or mineral sample from the site, treating the columns as protected heritage rather than an open quarry of curiosities. Access is deliberately kept difficult by the absence of a direct road link and the reliance on minibus and taxi relay from Sai Kung, a friction that functions as an informal visitor cap even without a hard ticketing system, protecting both the geology and the narrow dam-crest path from the kind of unmanaged foot traffic that has degraded more accessible sites elsewhere in Hong Kong’s country park network. The reservoir’s dual status as critical water infrastructure adds a further layer of restriction: sections of the surrounding catchment area remain off-limits to the public entirely, prioritizing water security over recreational access.
Practical Information
Reaching the site requires a multi-stage transit connection starting from urban transport hubs. Commuters typically take the MTR to a Kwun Tong Line station such as Choi Hung, then transfer to a green minibus route running to Sai Kung town center. From Sai Kung, travelers generally continue by green minibus or licensed New Territories taxi toward the High Island Reservoir East Dam, since general vehicular access into the restricted zone along the dam road is limited. Hiking enthusiasts often connect via Stage 2 of the MacLehose Trail, Hong Kong’s oldest and longest long-distance trail, which crosses directly over the crest of the East Dam and continues on toward the beaches of Long Ke Wan and, further along, Sai Wan and Tai Long Wan — making the reservoir as much a hiking waypoint as a destination in its own right for anyone tackling the MacLehose Trail’s early stages out of Sai Kung. New Territories Green Minibus Route 9A runs directly between Pak Tam Chung and the East Dam on weekends and public holidays, the most direct dedicated service to the site.