Editing Skill Descriptions (section)

==SWIM== 
STR
You can swim and maneuver underwater.
Check: A successful Swim check allows you to swim one-quarter your
speed as a move action or half your speed as a full-round action. If the
check fails, you make no progress through the water. If the check fails by
5 or more, you go underwater. If you are underwater you must hold your
breath to avoid drowning (see Suffocation, page 168). The DC for the
Swim check depends on the condition of the water:
CONDITION DC
Calm water 10
Rough water 15
Stormy water 20
Each hour you swim, make a Swim check (DC 20). If the check fails, you
suffer from fatigue (see page 167). Unconscious characters go underwater
and immediately begin to drown.
• Rescuing: Rescuing another character who cannot swim (for whatever
reason) increases the DC of your Swim checks by +5.
Action: A Swim check is either a move action or a full-round action, as
described above.

[[M&M Revised (v1.5) System Resource Document]]