Theo covered that well. I'm convinced another fish species is good at reducing snails too, provided they are the species of smail that can easily be crushed. (Bill Cody has been to my ponds and says I have two species -- one the fish like and one they do not) That species is the yellow perch. I caught a 15 1/4 inch 2 lb. 1/2 ounce specimen through the ice that passed a snail shell. Since my last planting of yellow perch I have seen a marked decrease in the amount of snails.

I also put up stakes with bright yellow braided line strung in three or four rows around the pond to discourage herons from wading in. The one that kept landing my my pier and I couldn't discourage has strangely disappeared. ;\)

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.