The body of a woman was discovered on the shore of Lake Brienz in the canton of Bern in December 2014.
But despite investigations in Switzerland and abroad, including an examination of missing persons cases, as yet the woman hasn't been identified, Bern police said in a statement on Wednesday.
Police think the woman may have died several decades ago, falling in the upper part of Lake Brienz or one of its tributaries.
The woman is said to be light-skinned, aged between 30 and 50 and 160-170cms tall. She was wearing light-coloured stockings and suspenders at the time of her death.
The cause of death has not been established, and there is no indication that anyone else was involved.
The public prosecutor is asking the public to come forward if they have any information, particularly if they know of any woman who went missing decades ago and whose disappearance was not reported to police at the time.
Anyone with information should call 033 227 61 11.