I do a decent amount of lane swimming, and at times I get bored on longer swims. Was looking on and off for a while for some method of listening to music while swimming. I ended up testing out one of those waterproofed iPod shuffles with wired in ear earphones. It seems to do the trick, iPod clips onto the back of my goggles, and the cord for the earphones are short and have tips that tend to do a good job of keeping a watertight seal in the ear. Once in a while one of my ears would get water in and the sound is useless at that point.
I’d love some sort of wireless waterproof buds that could connect to the watch, but with water any RF is probably a lost cause. I’ve kept an eye on the Bragi Dash since last year as they’re wireless in ear buds, they’re waterproof, and they can store audio files on the buds themselves for swimming.