Meaning:
"污" means "dirty." However, Chinese people in the past don't use the phrase this way. It's more likely a common usage originating from Japanese, where the character means "cheap, mean, unsightly or obscene." Chinese netizens now use the term a lot, chiefly in place of a similar slang "太黄" (literally: too yellow), that refers to something extremely obscene.
Example
A: 听说你们家对面楼顶有人锻炼身体？
Tīngshuō nǐmen jiā duìmiàn lóudǐng yǒurén duànliàn shēntǐ？
I heard someone is often exercising on top of the building opposite your home?
B: 是啊，我都不敢拉开窗帘。常常有个大叔裸身锻炼。
Shì a, wǒ dōu bùgǎn lākāi chuānglián。Chángcháng yǒu gè dàshū luǒshēn duànliàn。
Yeah. I dare not draw open my curtains. There is often an old guy working out naked.
A: 天啦，这画面，想一下都觉得太污了。
Tiān la, zhè huàmiàn, xiǎng yīxià dōu juédé tàiwūle。
OMG, I can't picture this. It's obscene!
(Edited by Stephanie Yang)