Officers say the body was found in the river at North Delaware Avenue and Orthodox Street just before 7 p.m. in the city's Bridesburg neighborhood.
The body of a man estimated to be in his 40s or 50s was spotted in the water by a ship.
Passengers onboard reported it to the U.S. Coast Guard.
Officials retrieved the body and stated it had been decomposing for several days.
Police say the body will be transported to the medical examiner's office.
There is no word yet on the man's identity.