Calm Water

This incantation inhibits natural or magical disturbances in water within its area of effect. Aquatic or water-based creatures with fewer Hit Dice than the caster's level flee the area if possible, and water-based creatures (water weirds, elementals, etc.) of this type cannot form. Aquatic and water-based creatures whose Hit Dice equal or exceed the caster's level must make a successful saving throw vs. spell to form, then save each round to operate in the affected area. The effect moves with the caster. (Note that while this spell would calm the waters of a hurricane, it would not affect the gale-force winds.)

The material component is a drop of oil.