Unfortunately, although it is a beautiful snake, Mud Snakes are generally not good candidates for captivity. Babies will sometimes take tadpoles and small plethodontid salamanders, but the adults will usually only take amphiumas or sirens. It is difficult to keep a steady supply of these items for food. I did, however, know one person years ago that kept one for years and fed it (of all things) hot dogs. This was something unique about that particular snake, and I've never seen another one take anything other than amphiumas and sirens. Mud Snakes spend most of their time buried in mud or in the water, and probably will not do well in captivity unless provided mud and water and a dry place to come out at night and prowl (they are largely noctournal animals), as well as their natural food.
I think your best bet is to photograph it, release it where you found it, and find something a little easier to care for.