To Become Muddy
To Become Impure, To Become Cloudy
intransitive verb, godan verb
You already know that 濁す means "to make muddy," but this is when you're the one getting muddy. It means to become muddy.
This has the same reading as 濁す. If you can remember that one, you should be able to remember this one.
煙草の煙で部屋の空気が濁っています。
The air in the room is getting cloudy with tobacco smoke.