South Dandalup Dam is a dam in Western Australia. It is located where the South Dandalup River flows out of Lake Banksiadale. The dam was built in 1971 in response to rapid population growth in Perth, Western Australia's capital city, and a resources boom in the Pilbara. The dam was officially opened in 1974. With a reservoir capacity of 137.7 GL, it is the second-largest dam providing water to Perth. It has a catchment area of 311 km2, a surface area of 21 km2 at full storage, and a reservoir length of 22 km. The dam itself is an earthfilled embankment dam, 43 m high and 268 m wide. Located only 6 km north-east of the historic town of Dwellingup, and around 90 km from Perth, it is a popular recreation area. Western Australia's Water Corporation manages the area, and has provided facilities including picnic areas with gas barbecues, and a number of walk trails.