From LSWiki

Class: Athletic Skills
Attribute: Constitution
Pedagogy: Physical Training

The ability to swim.  Determines how agilely one moves underwater and whether one can successfully 
swim difficult waters; influences how much one can carry and still keep one's head above water.

Trainers

Wandering: Damon
Hanoma: Olaris Wanders
Losthaven: Pryderi
Quetlatl: Itozuma Wanders
Association required:
Guild required:
Coven: Halea
Justicars of Tyr: Edwin
Shapeshifters Maramar
Verynvelyrae: Sirinil
Quest required

Notes

• The amount that can be carried increases very slowly with swimming skill, and is based on total weight, not encumberance.

• Swimming is trained by either moving in deep water (if you get the message "You cannot keep your head above water", you are training swimming) or by combat in any water

• Swimming has a huge effect on combat skills in water. If the skill is under fairly skilled, this will be a negative effect.