Was swimming in a new 1.17 snapshot cave, and while my drowning bar was full, I somehow died, and the death message "death.fell.accident.water" appeared. Apparently it usually happens after falling, so I only reported due to the fact that I hadn't fallen or jumped into the water; I had been swimming for the past 1 or 2 seconds. It's probably lag related, or potentially due to the fact that my disc is almost full, but I'm not really a tech person, so I couldn't say.