What's wrong with my switch?

I don't know much about the Nintendo Switch, but what your describing sounds like a damaged backlight, i've seen it before in Chromebooks, and its exactly as you have described it, everything works but you can barely see it. Usually in a computer a damaged backlight means a bent pin or something. Best I can say is see if you can manage to check it out without causing further damages, depending on how comfortable you feel with possibly taking apart the screen.

Tyshaunda, it kind of depends where the water got into your switch. My first guess would be that your LCD has sustained water damage and replacing it will probably fix the issue, but if water got inside and onto the motherboard then there's the possibility of board damage.

Do you have a dock you can plug it into so you can see if it has a picture with a TV or external monitor? If so, that would support the argument that replacing the LCD will get it going again.

Update:

Ah, that's actually fairly good news; it suggests that the LCD itself is the only problem. On the Switch the LCD can be replaced separately from the digitizer (front glass), so it'll be cheaper than the complete assembly. iFixit sells the LCD if you want to support their repair efforts; here's a link to the part you need.

Nintendo Switch LCD: Replacement Display Panel

You can also find that screen available on most of the big retail sites like eBay, Amazon and AliExpress; here are a couple of examples; if you search around you may be able to find one even cheaper.

for Nintendo Switch Screen Replacement LCD Display Panel Repair Parts,Include Tempered Glass

Nintendo Switch Lite Lcd Screen Replacement - Original Replacement Switch Screen - Aliexpress

And of course a step by step guide to doing that replacement would be handy too, wouldn't it? They've got you covered there too.

Nintendo Switch LCD Replacement - iFixit Repair Guide

If you're happy with using it with the TV, there should be no rush to get it repaired; there's a small chance the LCD could recover once the liquid inside finally evaporates; I wouldn't count on it, but it is possible.

There you go; I think you've got all the information you need, so good luck with it and let us know how it turns out!