Clarendon Weir, Heritage-listed dam in Adelaide Hills, South Australia

Clarendon Weir is a concrete gravity weir across the Onkaparinga River in Clarendon, about 20 km south of Adelaide. Its wall is 15 m high and 83 m long, and the reservoir behind it holds 320 megalitres over 8.5 hectares. The wall was originally built with large blocks of Macclesfield marble.

The dam was built between 1894 and 1896 to address water and sewer issues in Adelaide as the city grew. The structure was heightened in the mid-1960s to increase its water-holding capacity and better serve the expanding population.

The weir's name comes from the suburb of Clarendon, where it stands on the Onkaparinga River about 20 km south of Adelaide. Its wall was first built from large blocks of Macclesfield marble, a local stone, before being raised in the mid-1960s. The site was added to the South Australian Heritage Register on 8 November 1984.

The dam is located south of Adelaide and can be reached by car through the surrounding hills. Visitors should allow time to walk around the structure and nearby grounds, which can be accessed from local roads.

The tunnel to Happy Valley Reservoir was dug through the hills using ponies and carts, not a wooden structure. Water still moves through it by gravity alone, and the reservoir has no other catchment; Mount Bold Reservoir, added in the 1940s, feeds the weir downstream.