Crítica

[aleCcowaN]

murky water = agua turbia ("1. adj. Mezclado o alterado por algo que oscurece o quita la claridad natural o transparencia." DLE, RAE)
murky business = asunto turbio
murky sky = cielo plomizo
murky image = imagen borrosa (not meaning just blurry here)
murky future = futuro incierto/sombrío(if expected to be negative)
murky past = pasado obscuro/dudoso
murky world of drug-dealing = infame mundo de las drogas
murky writing = texto críptico (obscure in meaning)
murky war = guerra sucia

In my previous post I wrote thinking within the scope of the OP and not the various meanings of the Spanish word turbio/a. We have here one of many possible cases of one of several meanings of a word in English matching one of several meanings of a word in Spanish, besides the collocations.

[ROBINDESBOIS]

Originally Posted by poli

Wouldn't agua turbia be a perfect translation for murky (turbid) water? I am sure I have heard agua turbia spoken.

yes, it is.