I recently dusted off the game after quite a while and started a campaign and I discovered that I no longer know how to swim underwater. I know its an old problem and that there was no instructions within the game and I probably asked this before but I couldn't find anything on either a web search or a forum search here. So, can someone go through this one more time?

Maybe this will help ;)
http://compgroups.net/comp.sys.ibm.pc.games.rpg/gothic-ii-gold-and-swiming/453267

Uhm... Space?

I don't remember exactly how it works but pressing space starts diving. To move forward you press/hold down space. To steer... i really don't remember, it was something obvious direction keys or mouse or something.

Switching from more or less two dimensional navigation to three dimanional is always a pain in the ass.

We'll see :) I kept reloading and trying a lot of keys (including space) but all I could do was go nose down/dive using the control key. May not have actually used the mouse (duh!) as per the link. Seems the "w" key makes me move. It was surfacing (and obvious problem) and turning that kept killing me.

It took me a long time to remember how to do this. Once you figure it out, it's easy.