In the Bedrock Edition, a possible bug (See MCPE-36793) exists where water is part of the underwater ruins’ structure. The water generates as waterlogged water inside the loot chest and another full water block sits on top of the loot chest. Go to MCPE-36793 to view an image of an underwater ruin that generated on land, which has an exposed loot chest that is waterlogged and has a single water block on it. I’m creating this issue as it probably exists in the Java Edition as well but I’ll need help from other sources. Treat this as the Java version of MCPE-36793.