Mia likes to blow bubbles in the water (weird, I know) and she also likes to dig holes. Today she dug a hole big enough she could get inside it. (Then I had to fill it back up of course) This ends up with her face and feet and everything usually covered in mud and filth after going to the park. She also likes to try to catch the minnows in the water and shoves her face straight into the muck.
Basically if there's a way to get muddy, she will find it.