Most sensible D&D heroes should not go ANYWHERE near water in armor as they are 99% likely to be attacked by squids, weresharks, krakens, elementals, scrags, and any other number of unholy abominations that would love to drag them in for a swim
Realistically (which D&D is not) wearing any heavy armor and carrying pounds and pounds of metal would be a drowning death sentence. At the very least, countless adventurers would have stripped out of their gear and left it at the bottom of countless subterranean lakes
Water breathing, a couple of ropes, and I'm a millionaire!
This and only this could be the sole objective of every adventure, to scavenge lakes and ponds like the heroes are searching for lost golf balls.