Plant it up with bog loving plants maybe a few branches laid over the top so animals dont sink too much and can clamber there way out

You really need to find a way of running the water from the spring way as the situation is going to get worse not better. Even planting bog loving plants is not going to hold the soil together in the long run.

I would dig it out againand make a new pond. You would have to fence it off to keep other animals out.

Plant it FULL of bog plants ,surround area with whip wood/small logs. Animals have been there already they know its there ,Enjoy this new area!