General:
* Dirty
* Soiled
* Grimy
* Slimy
* Grungy
* Filthy
* Squalid
* Mirey
Related to water:
* Boggy
* Marshy
* Swampy
* Slushy
* Waterlogged
Related to color:
* Dull
* Cloudy
* Opaque
* Murky
Related to sound:
* Muffled
* Drowned
* Unclear
Related to thinking:
* Confused
* Unclear
* Vague
* Ambiguous
The best word to use will depend on the specific meaning you are trying to convey.