50 meter!! Research agrees with the previous poster crab:
The Cold Truth | Vertical Magazine - The Pulse of the Helicopter Industry
He must have been an extraordinary, extremely well trained ice water swimmer then!
The article says that no ordinary human can swim, not even for 10 meters, in cold water (below 10 deg C). Even if you get out of the helicopter after a ditching and even if you are a good swimmer, the cold water will immediately put your body in a state of shock, and you
will drown (long before the cold can kill you through hypothermia). Now, here we are not talking arctic cold here, where the water temperature (Sergey to correct me if I am wrong) would rather be 3 deg C or less, than 10 deg C.