Interestingly, apparently in total three Tallboys were found unexploded at Sorpe dam in ´58/´59. The first one found in 1958 was defused 6th of Jan 1959, and this is mentioned in many sources throughout the internet.
BUT: the Reuters news video linked above has the headline "More Tallboys Discovered In Germany" with comment "Two more RAF 5 1/2-ton 'tallboy' bombs were found, Jan 19, in the drained Sorpe dam reservoir, North Rhine-Westphalia."
So its four tallboys with the polish one counted for, I reckon there must have been more. Or be more yet to be found.