Azralian's Vortex of the Deep

A surging vortex of rushing water extends from the point the spell is cast in, rising into a 10 ft. high and 5 ft. radius vortex of chilling water. The vortex's space is also considered difficult terrain to all creatures except for the caster.  

When a creature enters the vortex for the first time on a turn or starts its turn there, it must make a Strength saving throw. On a failed save, the creature takes 2d8 bludgeoning damage and 2d8 cold damage and is caught in the vortex until the spell ends. On a successful save, the creature takes half damage, and isn't caught in the vortex. A creature caught in the vortex can use its action to try to swim away from the vortex as described above, but has disadvantage on the Strength (Athletics) check to do so.

On subsequent turns, you can use your bonus action to move the vortex up to 20 ft. 

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the bludgeoning and cold damage increases by 1d8 each for each slot level above 4th.