This spell could be cast at least 90 yd (82 m) away, covered an area of at least 90 ft2 (8.4 m2) and lasted at least 45 minutes. Range, area, and duration could all be increased by more experienced casters. When cast, the region filled up with thick seaweed that slowed the progress of ships and sailing vessels that had at least half of their hull inside the affected area. Oar-powered boats were slowed even more than sailing vessels. If the speed of the vessel was reduced to zero, then the ship was entangled and could not leave the area for the duration of the spell.
Creatures swimming in the affected area were also slowed with possible entanglement and entrapment below the surface.
In addition to verbal and somatic components, this spell required the caster to have a small amount of seaweed and a few live brine shrimp, which were tossed into the water as part of the spell.