Hogwarts schooling

You freeze an area of water that you can see within range and that fits within a 5-foot cube. The area becomes difficult terrain for the duration. Each Medium or smaller creature that is covered, submerged or partially submerged in the affected water has its speed halved and must make a Constitution saving throw. On a failed save, a creature takes 3d8 cold damage, or half as much damage on a successful one.