When this spell is cast, a sea creature large enough to ride is summoned to the caster, if one is present within an hour's swim. Therefore, the summons cannot be answered until an hour has passed and the creature has had a chance to arrive. Typical sea mounts include giant fish, sea horses, sea turtles, and nonmagical creatures like rays and dolphins. Even sharks may respond and, for the duration, their natural predatory urges will be kept in check. The summoned creature can bear one person at the surface of the waves, and can carry the rider a variable distance depending on its reaction to the summons (see below).
When the spell is cast, the sea priest must picture where he or she wants the creature to go. Since this spell does not bestow the ability to communicate with sea creatures, only the mental picture provides direction to the sea mount. The DM should make a reaction roll: if friendly, the creature carries its rider to the nearest shore, no matter how distant. If unfriendly, it travels to somewhere near and abandons its rider as soon as possible. A creature that makes its saving throw can either ignore the summons, or deliver the rider to a destination of its own choosing.
Notes: Common for sea priests, otherwise very rare. (Updated from Dragon Magazine.)