I don't enjoy reporting this, but the fact is that each year when I go to the mikvah on Erev Yom Kippur, by about 2 -3 hours after the mikvah has opened, the water looks murky and disgusting. The mikvah rooms tend to look sloppy.
As I don't go to the mikvah other than Erev Rosh Hashanna and Erev Yom Kippur, I'm giving benefit of the doubt that this unhygienic appearance occurs only on these days. It shouldn't.
My bigger concern, though, is that these same mikva'ot are used by women, and they are open nightly. While the nightly volume is nowhere as busy as it is on Erev Yom Kippur, I am concerned about the general hygiene in mikva'ot for some of my friends and relatives. Some women have told me some "horror" stories about things that they've seen in the mikvah that really churn my stomach.
In a small town that has 1 or 2 mikva'ot, there's little choice of where women can go. But in a large city where there are numerous mikva'ot, I wonder if anyone has published a "rating" or evaluation of the health safety and appearance of mikva'ot. I would gather that the city or state health department inspects these places, also, no? If they do, I think they publish any findings.
As I told a M.Y.'er in a recent comment, if I were a different gender, perhaps, I would evaluate and publish my own rating in my own area, at least.