i know he can swim but has there been word if he can dive?
IIRC There is not going to be any diving and as other posters have stated, Swimming is going to be based on Geralt's current stamina. Horse swimming is unconfirmed at this point. Personally, I would love to see both implemented, whether at launch or in a post-game patch.
At the very least, I would like diving to be added in ( If presently it is not in the game? ) Then again,if CDPR were to add diving,that means every body of water that is deep enough to dive in,will need underwater development time. At this point, it may not be a priority for the Devs.
It would be a nice bonus but IMO it is not a necessity. There are plenty of other gameplay aspects( implementations,optimizations & expansions) that the team more than likely is concentrating on and considers crucial.