A man, 84, has drowned at Port MacDonnell in the south-east of South Australia.

The man, from Mount Gambier, was found in the water between Port MacDonnell yacht club and the caravan park about 6:00pm ACDT on Tuesday.

Those who pulled him from the water tried to revive the elderly man until an ambulance arrived.

He was taken to Mount Gambier hospital but died.

South Australia had a series of days with temperatures in the mid-to-high 30s until a change reached the state late on Tuesday.

Senior weather bureau forecaster Vince Rowlands said it also had been one of SA's longest spells of hot nights over the past 11 days.

"We'll see temperatures in Adelaide drop considerably for maximum and minimum temperatures, so certainly a nice relief from the hot weather," he said.

"Minimums we're expecting to drop down for the next few nights to around the mid-teens as well so much more comfortable conditions for the overnight periods."