Sargasso

This spell creates a mass of thick seaweed in a body of water, making it difficult to sail through. The approximate depth of the seaweed is 5 feet. The caster can create a 10 x 10-foot mass per level-about 35 feet x 20 feet at 7th level. Ships sailing through the weed have their speed diminished by 2 mph if they are sail-powered, or 3 mph if they are oar-powered. Ships reduced zero speed or less are entangled (as the spell), and unable to move. At least half the ship's length must be in the area of effect for its movement to be reduced. A large ship might not be affected by a small sargasso region, even if it sails right through.

Swimming creatures have their movement reduced by 6. Air-breathing creatures reduced to a move of 0 or less must make a successful saving throw vs. death or be trapped below the surface.

The material component of this spell is a small amount of seaweed and a handful of live brine shrimp, which must be tossed into the water.