When iron golem are in water the don't do anything like moving or attack and they don't float in water so that's a problem for me because I have 2 iron golems and they are in water so they are not useful (that means that I lost 72 of iron or 8 blocks of iron).
I believe this is working as intended. Quote from the wiki:
"When in water, they will sink, immobilize, and become passive, but will still be pushed by flowing water."