A woman who came to swim at the lido in Rodgau in Hesse has been missing since 20017.
Four years later, shortly before the lake opened, an employee has now discovered a corpse floating in the water.
It may be the woman, said a police spokesman.
The background is still unclear.
The corpse will now be examined in forensic medicine to find clues about the identity and the cause of death.
After the body was found, the police and the search for clues were on site, the city said.
The lake is due to open on Tuesday as planned.
According to the Offenbach Post, the missing person is a 64-year-old woman who was considered a good swimmer.
On the evening of her disappearance, only an abandoned bundle of clothes and the season ticket were found on the nudist beach.
apr / dpa
