1. To cover, fill, or contaminate something with mud. A noun or pronoun can be used between "muddy" and "up." I just got the Jeep washed, and you went and muddied it up offroading in the mountains! Take your boots off so you don't muddy up my carpets! They all went into the wading pool and muddied up the water.

2. To dredge up the mud at the bottom of a lake, pond, river, etc. A noun or pronoun can be used between "muddy" and "up." The lake is so perfectly tranquil and still—don't ruin that by traipsing in and muddying it up! We could have found your ring in this pond if you hand't muddied the water up before we started looking!

3. To render something awkward, confusing, and disorderly; to obscure or obfuscate something. A noun or pronoun can be used between "muddy" and "up"; often used in passive constructions. The introduction of new tariffs is likely to further muddy up the already complicated relationship between the two countries. They muddied the contract up with all sorts of misleading, cryptic language. Our roles within the team have become so muddied up that we've largely given up the idea of job titles.