Cherenkov radiation is something you are unlikely to experience in the natural world.This visible blue light is the “shock wave” produce when something travels faster than the local speed of light. The speed of light in transparent substances such as glass and water than be substantially lower than it is in a vacuum, so high energy particles can easily be FTL in those media.
Nuclear reactors generate just such high energy particles. And they are often immersed within pools of water for both shielding and cooling. Thus… Cherenkov radiation, and thus this spiffy collection of videos showing just how fast reactors start cranking out the rads upon startup.
Also:
https://www.youtube.com/watch?v=UxQdS0pbpKo
This sort of thing is unlikely to appear outside of a reactor environment. If you are in space, high energy cosmic rays that penetrate your eyeballs can create tiny flashes of Cherenkov radiation within the vitreous humor, an effect that astronauts have note since the earliest days of spaceflight, something sure to freak the fark out of space tourists. But these are instantaneous phenomena, not steady state ghostly glows. If you do stumble across something out in the wild causing the water, air or glass around it to glow like Dr. Manhattan, you may well have stumbled across something that it would be best to stumble away from.
And as to how good that water shielding is? Your average human would probably look at that Cherenkov radiation and assume that the water ain’t doin’ diddly. But things like electrons *aren’t* photons, and they don’t pass through water as easily as simple light does. This “What If” from XKCD explains it well.