Scuba
Defaults: IQ-5 or Diving Suit-2.
Prerequisite: Swimming.
This is the ability to use self-contained underwater breathing apparatus (scuba). Roll when you first enter the water, and again every 30 minutes thereafter, to avoid inhaling water (treat as drowning; see Suffocation). If you know this skill above default level, a successful roll also lets you spot problems with the equipment before you put it on.
Modifiers: -2 to -4 for unfamiliar scuba rigs; e.g., closed-circuit gear when you're used to open-circuit.