She was reported missing just after 3pm, and was located south of Brighton about 6.40pm.
Sergeant Kevin Davidson, of Mosgiel, said the woman, of Malaysian and Indian descent, had been fishing with her son-in-law in the Taieri River near the start of the track at Henley.
He said the son-in-law was distracted by his fishing, and did not notice the woman had walked off.
There were concerns for her safety because she was prone to hypoglycaemia (low blood sugars) and had dementia.
Sgt Davidson said two police search and rescue teams were dispatched to search the track - one from the Taieri Mouth side, the other from the Henley side.
A police search and rescue dog was also working with one of the teams, and four boats were used to search the Taieri River, he said.
A police spokeswoman said it was believed the woman walked the track to Taieri Mouth and then along the beach towards Brighton.
