The kids, 12 and 14 years old, found the remains in a bin bag at the banks of the river in Cologne on Wednesday afternoon, police report.
All that was left was a torso. The head, arms and legs were all missing.
It is believed that the bag, which had been tied shut, washed ashore at the point near the Zoo Bridge where the two adolescents found it.
A man who was walking his dog along the bank at the time and also saw the body told Express: “It is a male corpse around 40-50 years old, tied up in a blue bin bag."
Police have now started a murder investigation and the body part has been sent for a medical examination, which investigators hope will provide clues about the man's identity.