Where to place a camera to record Swimming
For the swim you really only have one option - to wear a light helmet of some kind to get the camera on the top of your head.

Anywhere else and it will not show anything useful (too much splash) or will cause drag (eg chest mounted) - look how much of the body is underwater:



If you think you are really good, point it backwards. You will get a better view, with less splash, and if you are in front, the shots you will get of the rest of the pack could be really good.