We have a farm pond very similar to yours. The water appears murky, but is actually quite clean if you dip out a container. Depends on what your soil is. We also have an island (which we did NOT want but the guy who dug the pond apparently decided otherwise...) which increases the amount of silt. We've let it just grow in naturally, planting some natives along the banks now and again. If your cows will have access to the pond, think about bringing in some gravel and establishing an area that is easy for them to get to the water. Otherwise, they will trample at will. Does your pond have a source of fresh water? Ours is fed by a creek, which is helpful for keeping it clean and less mosquitos. Be cautious of introducing invasive water plants - we made that mistake with yellow flag iris. I'd recommend planting natives, easy enough to get a list from your county extension. Have fun!
