The 95-year-old Baroota Reservoir is overflowing after heavy rain in the district.
The dam was built in 1921 to supply water to Port Pirie and other northern parts of the Beetaloo distribution system.
Although wet weather delayed its construction, several dry years followed its completion. It wasn't until 1932 that the dam held enough water for the spillway to overflow.
Since the mid-1980s, the reservoir has spilled five times.
An SA Water spokesman said this included the latest spilling event which began in late September. Before this, water levels had not reached capacity since 2001.
The dam was originally built with a stone-pitched spillway, but because of damage to the structure in the mid-1950s, a concrete-lined channel was created. In 1974, the channel failed and a new spillway was built in 1978.
The reservoir is offline – not supplying drinking water to customers – but is used for some small irrigation purposes. The dam is on the Baroota Creek to the north-east of Port Germein.
At capacity, Baroota holds 6140 megalitres. This time last year, the reservoir was at 3060 megalitres. The reservoir’s wall is 301 metres long and 30 metres high.
Overflow from the dam enters Baroota Creek which eventually reaches the sea at Port Germein.
Local residents say this has increased tidal surges.