The car was found on 30 June and recovered the next day, but details of the find have only just been confirmed.
Police diver DS Nick Sawdon said: "It was half full of sand so we had to use lifting bags and winches to recover it."
A family of eels was found living in the car's footwell, he said.
The Capri was built by Ford of Europe from 1969 to 1986, gaining a major following due to appearances in TV shows such as the Professionals.
A police spokesman said the car, if sold in pristine condition, would be worth about £15,000.