Drown

You cause a creature's lungs to fill with seawater. Unless the target makes a successful Constitution saving throw, it immediately begins suffocating. A suffocating creature can’t speak or perform verbal spell components. It can hold its breath, and thereafter can survive for a number of rounds equal to its Constitution modifier (minimum of 1 round), after which it drops to 0 hit points and is dying. Huge or larger creatures are unaffected, as are creatures that can breathe water or that don’t require air.

A suffocating (not dying) creature can repeat the saving throw at the end of each of its turns, ending the effect on a success.