Up to 6 rounds
A wall of water springs into existence at a point you choose within range. You can make the wall up to 300' long, 300' high, and 50' thick. The wall lasts for the duration.
When the wall appears, each creature in the area must make a Str saving throw. On a failed save, a creature takes 6d10 bludgeoning dmg, or 1/2 as much dmg on success.
At the start of each of your turns after the wall appears, the wall, along with any creatures in it, moves 50' away from you. Any H or smaller creature inside the wall or whose space the wall enters, must succeed on a Str saving throw or take 5d10 bludgeoning damage. A creature can take this dmg only once per round. At the end of the turn, the wall's height is reduced by 50', and the dmg creatures take from the spell on subsequent rounds is reduced by 1d10. When the wall reaches 0', the spell ends. A creature caught in the wall can move by swimming if they make a successful Str (Athletics) check against your spell save DC. If it fails the check, it can't move. A creature that moves out of the area falls to the ground.
Sie Altum Fluctus Maxima