I like A and B options! Option C might come into play after the re-working. My guess is that your "stocking" from someone "just" wanting to sell fish, was little more than fish food for the starving bullheads. Those bullheads are most likely also the cause for such low clarity in the pond due to their constant muck rooting looking for food.
If you want to drain the pond, don't worry about bacteria for the sludge. Best method would be to get a back, or track hoe to breach the dam and keep it drained. It sounds like you would like a larger pond, and it will be less expensive to push the old muck out to be used as filler on the back side of an entirely new, cored and WELL compacted dam. This will gain you volume and a little more depth if wanted in areas at the lowest price/least equipment hours.
What should you be googling?!?!?! Nothing! Stay here and brainstorm on PondBoss! lol Take pictures too!
