Rising Water

You conjure a cylinder of calm water on an area of solid ground or on top of a body of water. The water forms quickly but displaces only air; it doesn't push away objects or creatures, though anything in the area when the spell is cast is submerged. Unconscious air-breathing creatures caught in the area immediately begin to drown, but other air-breathing creatures can hold their breath while in the cylinder. Movement through the cylinder at normal speed requires a successful DC 10 Swim check (otherwise, creatures move at one-quarter speed). If conjured in an area with insufficient room for the entire cylinder, the cylinder attains its maximum possible size. It retains its shape in defiance of gravity for the spell's duration, and any creature can enter or exit the cylinder's sides as easily as stepping into or out of a pool of ordinary water.

The water disappears at the end of the spell's duration, so creatures swimming in the water immediately fall to the ground.