Swim

Basic, Movement
Strength
The Swim skill is used to swim and dive. Swimming under normal conditions does not require a Test. However, Tests may be called for when waters are rough or when swimming for an extended period is required. For more information on the Swim skill, see Swimming.
The Swim skill assumes a character is attempting to swim in water, but on alien worlds a character might encounter unusual substances such as lakes of sulphuric acid. The Difficulty of the Test might be increased to represent particular conditions. Swim does not protect a character from harm when swimming in toxic or otherwise dangerous liquids, nor does it negate the need for protective clothing.
A Swim test is a Free Action made as part of a Move Action.

Aquatic Combat

Whenever you fight while submerged in water, all Weapon Skill and Ballistic Skill Tests take a –20 penalty. As well, you must succeed on a Swim Test to move in this environment. When you Test your Swim skill, and you get two or more degrees of success, you reduce the Difficulty of your attack Tests to Difficult (–10).

Hiding Underwater

You can hide from a pursuer on land by diving into a body of water and waiting below the surface until they have passed by. If you do this you may use your Swim skill instead of Concealment.

Life-Saving

When another character gets into trouble in the water, you can dive in to help him out. If you reach the struggling character, you can pull him to safety by succeeding on a Swim Test, but the Difficulty worsens by one-step for the added bulk.