I have -0- experience with stock ponds, but quite a bit of experience w/ water garden/fish ponds. Don't know what your input/fill situation to the pond is. You can make a big dent in the really yucky, string algea by running your input water through barley straw. If you can, put a couple bales, or barley straw in heavy netting, at the point the water feeds into the pond. Just let the water hit it and run through it. The shorter types of algea are just natural -- sun + water + algea. Some fish types will keep that down or there may be some herbicide you could use, but make sure it won't mess up your stock. Mud is something else, and can't give you suggestions about that.
In a stock tank, a few feeder goldfish can help keep algea under control, but probably won't help you in a pond or pond dam situation.