Jake, if your not ready for total renovation, then start off small steps in learning how to take care of it the way it is now. I would get a minnow trap and catch what you can. Take pics, and post them for identification. Fish the pond in all different ways, times, approaches, and see if you come up with bigger ones that won't be in the trap. You might have a nice little pond and not even know it till you do these basic things. If your a pond owner, you will need to invest in a trap anyway, might as well be now.