We can't guarantee you'll have this opportunity - but some of you will.  Our son was in the Galapagos on the Samba (this was already 2 years ago), and the ship came across a very large group of dolphins (not too uncommon in Galapagos).   Juan Manuel Salcedo, the Samba's principal guide (and co-owner) ordered all engines stopped, and suggested that people might want to jump in and "make like a dolphin".  Our son was an enthusiastic participant and managed to make this video of his experience.