“South African Police Services search and rescue teams will take up the search at first light on Sunday,” they said in a statement.
Dennis had gone missing on the opening day of the annual open water swimming event near Howick in the KwaZulu-Natal Midlands.
“Dennis was swimming in the company relay race and entered the water at 11:22:35,” the organisers said.
“There was no record of him exiting the water at any place along the race.”
Concerned friends, who were swimming with him, alerted officials after waiting for more than an hour for him to emerge from the water.
The event’s medical facilities were checked, and lifesavers confirmed he had not been pulled out the water.