Paramedics were called to Port Noarlunga Jetty at 1.20pm on Friday following reports a woman had been bitten by a shark.
The 32-year-old woman was initially said to have suffered life-threatening head injuries.
Her condition was later updated to serious but not life threatening, according to SA Police.
The victim was rushed to the Flinders Medical Centre and is in a stable condition, an SA Health spokeswoman said.
Emergency services evacuated people from the water to search for the shark but have since reopened the beach after no trace of the animal could be found.
The suspected attack marks the third shark-related incident in two months in South Australia.
A 55-year-old man surfing at Granites Beach on the state's west coast on October 31 disappeared and is believed to have been taken by a shark.
The man's surfboard was all that remained of the attack, witnesses said.
Pamela Cook, 64, was taken to Mount Gambier hospital in a serious condition after a shark bit her leg at Beachport on South Australia's southeast coast on October 2.
The incidents follow the suspected fatal attack of 46-year-old teacher Simon Baccanello in May who disappeared without a trace while surfing at Walkers Rock Beach, about 365km west of Adelaide.
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