Striking wave was a divine magic spell available to priests of Umberlee, the Bitch Queen. It created a large wave in a body of water that could be directed by the caster and heavily damage or destroy creatures, objects, vessels, and structures.
Some part of the caster's body had to be in contact with a sufficiently large body of water for this spell to be effective. When cast, striking wave formed a large swell of water 10 to 100 ft (3 to 30 m) wide as chosen by the caster. The wave traveled in a direction indicated by the caster and the course could be changed but required the caster to concentrate at the expense of doing anything else. The point of origin of the wave had to be within 105 ft (32 m) of the caster (more experienced casters could extend this range) but the wave could travel for several miles (kilometers) before subsiding harmlessly.
In order for striking wave to do damage, the last 60 ft (18 m) of its journey had to be in a straight line for it to build up momentum or else objects in its path merely rode the swell of the wave or the impact was nothing extraordinary. However, when a fully formed striking wave encountered objects, creatures, or obstacles, it had the potential to do a massive amount of damage. Free floating objects and creatures got one chance to resist this spell which, if successful, reduced the potential damage. Creatures that could swim and had freedom of movement in the water got a second chance to resist, which further reduced the potential harm. Ships at anchor or moored at a dock suffered some structural damage that made them less seaworthy. Ships at sea took only half this damage. Smaller boats took twice as much damage as larger ones in all circumstances. Open vessels and barges were subject to possible capsizing.
If the striking wave was cast into a confined body of water with a natural or constructed sea wall, like a harbor, and it struck this solid, immobile barrier within 100 ft (30 m) of its origin point, then the striking wave reflected off this obstacle and continued in a new direction with full force. Vessels, creatures, and objects in the path of this reflected wave had to attempt to resist the spell as described above, even if they already managed to resist some of the devastation from the original wave.
If the striking wave hit a shoreline, then objects, structures, and creatures at the shoreline were subject to the full power of this spell, but for every 10 ft (3 m) the wave traveled inland, the maximum potential damage was reduced, until it was finally reduced to zero at 100 ft (30 m) inland. Structures built to withstand storms and storm surge obviously fared better than those that were not.
In addition to verbal and somatic components, this spell required a drop of water blessed by Umberlee herself, or one of her senior priests in her name.