In this seed, I found a tiny patch of either ocean or a flooded cave connected to a river, which drains into an even smaller pool of water and finally under a mountain. I found it at co-ords -406 82 -1177 on seed -7962106743335640204. Found originally in 1.21.1, it works in Java Edition up to 1.21.10, and even Bedrock Edition with a few minor changes.
by Fabulous-Rough-3460