Throughout the module, a number of areas exist where it is possible to enter a body of water to explore beneath its surface. While submerged, a character faces the risk of drowning if he or she remains below the surface too long. The length of time a character can spend underwater is determined by his or her Constitution ability score: a character can hold his or her breath for a number of rounds equal to his or her Constitution score. Thus, a character with a Constitution score of 10 can hold his or her breath for a minute of real-life time before he or she runs the risk of drowning. The system will alert the the player periodically as the moment of drowning draws closer.

Drowning is handled in accordance with the 3.5e Player’s Handbook rules for drowning: if the character is submerged for a number of rounds beyond their Constitution score, a DC 10 Constitution check is made each subsequent round that the character remains underwater. If this check is failed, the character begins to drown.

While underwater, the character also suffers a number of penalties to movement and combat: the character’s movement is slowed, he or she is effectively rendered silent as though under the effects of a Silence spell, his or her attack modifier is decreased, and damage from slashing and bludgeoning attacks is reduced. In addition to these penalties, characters cannot use thrown weapons and whips while underwater and torches are rendered useless.