Requites the a body of water of at least a 5ft sphere witching the casting range
The water whips up around a 10 ft. Cylinder that reaches up 10 feet tall and crushes all those inside. Those inside of the casting range take 6d6 bludgening and must make a constitution saving though. If they succeed they are able to escape the cylinder of water, if not they are considered restrained by the water. And their movement speed becomes 0ft. If a creature remains restrained for 5(+ restrained persons con modifier) they go unconscious. And if they stay in the cylinder when they make a death saving though they have dis-advantage
All non-magical fires in the spell radius are extinguished as well. All magical fires that are below 3rd level spells are extinguished as well
At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd. And after 5th level spell slot the water can come from the air or the plants in the ground.
This spell seems a bit too powerful for a 3rd level spell. Also, you put the damage at the top (the search criteria) as fire damage. You also seem conflicted whether they should make a Constitution or Dexterity saving throw . . .