Boating equipment and Mr Higgins' wallet and keys were recovered near the Murray Mouth on Wednesday, two days after SA Police received a distress call from waters off Victor Harbor.

The search has so far covered more than 500 square kilometres, from Encounter Bay to Cape Jaffa.

Operations Inspector of Hills Fleurieu LSA, Gus Sickerdick said it was unclear if Mr Higgins had deliberately set sail, or been blown from moorings in rough conditions in the early hours of Monday morning, September 21.

"We are still investigating the circumstances and what has gone wrong," Mr Sickerdick said.

"Our patrols have searched from the Mouth to the Goolwa Beach Surf Rescue [Club] and have found a number of pieces of debris which will form part of the investigation.

"The search will continue and our fixed wing aircraft will continue its runs. We cannot currently carry out sea searches because conditions are too rough."

According to Mr Sickerdick, the search and rescue operation is expected to be reassessed at lunch time today.

The search effort comes less than two weeks after Mr Higgins and his crewmate Derek Robinson were rescued after spending more than four days missing at sea, in the state's largest ever sea rescue operation which covered over 104,000 square kilometres.

The pair were discovered in Salt Creek before being towed to Victor Harbor, where Mr Higgins had remained anchored since.

He and the Margrel were last spotted at about 3pm on Monday, September 21, anchored off Granite Island, when a weather warning was declared for the region.

Mr Robinson revealed Mr Higgins had been the victim of ongoing abuse while moored in Victor Harbor.