This trap will create a pool when triggered. Flying or levitating over it will not set it off, so water walking is the only way to trigger the trap without falling into the resulting pool. Successful #untrapping will create the pool on your square instead of the trap location, and so is not recommended. Gremlins will intentionally trigger the trap and use the pool to multiply.
Generation: Never randomly generated above dungeon level 5.
To remove: Set it off or get a monster to do so, then push a boulder into the pool to fill it in.