Cast your rig upstream of the dam and let it roll down to the dam and in front of the face. One key thing is not to let them sit to long in front of a dam as Willow cats will swim directly into the rocks. They love to hide, and in between rocks is a favorite spot.
I run a barrel sinker above a swivel with about an 18″-4′ leader and then a #2 hook. When you get a hit, let them take it a little bit as they will often bite them about half way up (even big fish). I had one bite the guts out of a cat on Sunday.
I rarely let one sit as they tend to get hung up, and at almost $1.50 each I don’t like loosing them. Most of the big fish I’ve caught on Willow Cats have come about 10-20 yards in front of the dam.
Also, be prepared to retie a lot of times when you first get started. I rarely ever use bigger than 1/2 oz and in the dead of summer usually use 1/4 oz even 1/8. You want the rig to move just a bit (the best is when it drifts when you lift it only).