The dam at Lake Benmore is the largest dam within the Waitaki power scheme, located in the Canterbury Region of New Zealand's South Island. It is the largest earth-filled water-retaining structure in New Zealand and one of the largest earth dams in the southern hemisphere. Its core is an impermeable clay-like gravel, supported by two massive shoulders of river gravel. Lake Benmore has a volume of 12.5 million cubic metres, holding about 1.5 times as much water as Wellington Harbour. The dam's spillway can cope with 3,400 cubic metres of water per second, about 10 times the mean river flow. With a generating capacity of 540 MW, Benmore Power Station is the second largest hydro station in New Zealand.