Police and emergency services are searching for a swimmer in the water off Parsons Beach, near Waitpinga, on the Fleurieu Peninsula.
The alarm was raised just after 12.30pm on Tuesday 15 January when two swimmers appeared to be caught in a rip and swept out to sea near Waitpinga.
Emergency services rushed to the area and commenced searching by land, air and sea.
One swimmer was able to get back to shore, the search continues for the second swimmer.
The Police Helicopter (PolAir) Sea Rescue Squadron and several local boats are assisting in the search.