Remember that niggun that would be mockingly sung with the words: 'why'd 'e die did 'e die did 'e die 'cuz there's a shark in the mivkah'? It's a true bungalow classic (the tune is actually called the 'Belzer Hakafah').
But it turns out that he didn't die because of any sharks, but because a towel closet was blocking the emergency exit (Link). Y'know, government building codes regarding public construction are not just about making the ehrliche Yidden spent more money or cut corners. They actually make sense, most of the time. Moreover, lack of regulation does not absolve the deployment of common sense. A men's mikvah is quite obviously a potentially hazardous place in the immediate sense (although slower developing problems, such as PTSD for victims of pederasty and athlete's foot for the rest of us, certainly should give one pause); slipping, drowning, and choking on popcorn are just a few of the dangers that lurk in the mildewed corners of the men's mikvah. Caveat dunkor.
Let's all remind ourselves that in 99.99% of all instances (with the exceptions of le-shem geirus and to ascend Har HaBayit) there is no mitzvah - chiyuvit or kiyumit- for a man to immerse in a mikvah. That favorite chapter of Messilat Yesharim, the one entitled 'Be-Mishkal Ha-Chassidut' rears its head again. Read it and read it again.
Geez, I'm starting to sound like Harry. Good thing I'm keeping this short.