Goldfish like Koi will scrounge around on the bottom looking for food. Sucking up muck and spitting it out. Just like they do in an aquarium. Koi however are able to reach larger sizes than your standard goldfish.....thus could stir up more! Although I have built and maintained many a garden pond over the years, and find the Koi to be beautiful fish....I still consider them to be a Carp (which is the family they come from). And I consider Carp to be the Devil! \:D

Bullheads and Carp are the devil~