Surface level creature drowning trap

In my survival games I haven’t found any dungeons yet so I’ve decided to make myself a surface creature trap. The way it works is there’s a flow of water across the top of the hill leading into an enclosed waterfall with only a single block high gap at the bottom. Creatures fall in and failing to swim up current get dragged under in the waterfall. After they die, they usually drop some loot which then flows out of the bottom ready to collect. I keep that hilltop unlit and so far I’ve been able to catch quite a few mobs.