Local photographer Jon Galpin was taking photographs of what he thought was an osprey at Fishery Bay last month when he realised the markings were not quite right.
Mr Galpin realised the markings around the eyes of this particular bird were not like an osprey.
"It was with that that I realised it was a white belly sea eagle, an exceptionally rare sighting as their population is said to be in a parlous state and endangered," he said.
"It was definitely hunting, it didn't appear lost.
"From what I've read, it said there are only two known nestings in South Australia, one in Renmark and one on the Fleurieu Peninsula.
"I'm extremely lucky to have seen it...the closest I got was about 15 or 20 metres.
"I did see it again during the week and it's definitely a sea eagle."