I played Nethack all day. I drowned to a giant eel attack on the quest level. I had two blessed luckstones, the amulet of reflection from Sobokan, I used a genie wish to get a ring of slow digestion, and I had cleaver from sacrificing. None of that helps protect from simple drowning, though. Dumbness. I even had a can of grease in my backpack. Extra dumbness.
Next time I'll wish for a coupla blessed scrolls of Genocide. Defend yourselves from that, you fucking eels.