Witnesses reported seeing the man and infant go over the edge of the Whispering Wall at Williamstown, north of Adelaide, on Wednesday afternoon.

The man was found dead when police arrived, while paramedics were unable to save the baby girl.

The Whispering Wall is the retaining wall of the Barossa Reservoir, with the 36-metre high structure built between 1899 and 1903.

The popular tourist attraction was bestowed its name as words whispered on one side can be clearly heard at the other, more than 100 metres away.

"Children in particular love visiting the wall and testing its abilities," the official Whispering Wall web page says.

Local detectives and forensic crime scene investigators have attended the scene to examine the circumstances surrounding the incident.

"At this stage, no one else is being sought over the deaths," South Australian police said in a statement.

"Police will be preparing a report for the state coroner."

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Australian Associated Press