Swim is an ability that does exactly what you would expect. Swimming was rarely learned by members of ancient societies except by those who worked on boats and ships; and even then it was not guaranteed that a sailor could swim. A single level in swim allows the character to do more than merely wade or jump along the bottom when in water. Higher levels in swim increase the speed of swimming by increasing the effect of strength and land speed on swimming speed.
Recently in one of our test campaigns, a simple flooded fortress became quite the puzzle when it was realized that no one in the party could swim. It can be a good investment for a character who doesn’t want to be caught up on simple obstacles.
Fighters, Druids, Bards, and Rangers are able to get Swim. It is a common backstory ability for characters who live near water or in the wilderness. It can also be earned cross class from the Master Weaver with a little practice.
Hold Breath is another useful ability for the water. While any player can hold their breath for 6 seconds per point of Constitution, levels in hold breath add 30 seconds each for the first 6 levels, then 20 seconds thereafter. This time is until the diver passes out from lack of oxygen, but even so, just a few levels in hold breath are enough to make a Mind Weave hero a world class diver.
Druids and Rangers, the hard core wilderness classes, get Hold Breath. It is more rare than swim as a backstory ability, and it is hard to justify as a Master Weaver ability, but it is certainly possible.
Would you be willing to sacrifice some minor abilities to be an aquatically adept character? What about including it in your backstory? How does it affect puzzle design if none of your players can swim? Comment below to let us know.