The watch makes this a good story; swimming up the Thames isn't that extraordinary. The beluga (a whale living in the Arctic) nicknamed Moby Dick that swam 300 km up the Rhine certainly bests that:
"On May 18, 1966, a few Rhine skippers near Duisburg reported a white whale in the Rhine to the water police. They reacted by first making the mariners take a blood alcohol test, which came up negative"
"On May 18, 1966, a few Rhine skippers near Duisburg reported a white whale in the Rhine to the water police. They reacted by first making the mariners take a blood alcohol test, which came up negative"
(https://en.m.wikipedia.org/wiki/Moby_Dick_(Rhine). Video at https://www.youtube.com/watch?v=JFBGhB-APMs. This beluga apparently was on board a ship that sank while carrying it to England)