Sponge Bob is a fly that has been developed for catching cob. The fly should be fished on a sinking line in deeper water, over a sand bottom. The line can go all the way to the bottom, and the foam in the fly will keep it off the bottom. It represents a baitfish keeping close to the bottom to avoid predation. Cob generally feed in this zone. Sponge Bob Fly is a very effective pattern.