I manage a Dive Resort in Indonesia, and my cat has had to be able to swim. Neo goes for a swim every two days in the ocean. Afterwards we give him a hot bath with shampoo to wash off the salt water. He never complains, never tries to scratch us, never tries to run away.
Enjoy Neo, the Swimming Cat!!!
I would like to add that we have had many guests staying with us who are vets, and none of them thought he was ever upset, annoyed or scared. We would not do this if we thought it was causing him any harm or discomfort.