I have found that the structures for Underwater Ruins have the solid blocks treated as water logged such as the stone bricks, mossy variants, and even the gravel or sand at the base of the structure are water logged. This creates inconsistencies with what blocks should or shouldn't be water logged. I tested this out on icebergs and basic underwater terrain and did not find them to be water logged. I could even use an empty bucket on gravel to pick up water. The blocks would need to be mined up and replaced in order to create a viable air pocket in with these structures in tact under water. I've searched for other reports of this but I haven't seen any so I figured I should report this one myself. I'm more experienced with the Java version of the game but wanted to try Minecraft on my Switch so I figured this to be a bug worthy of attention.