Typically 20 feet of water in a river is out of reach of most fly fishermen. But if you want to try, you can try a shooting head of Cortland LC-13 with either Amnesia or a braided mono running. I'm not sure that it would go down in your currents, but it is your best shot. I would use a heavy rod with this, 8, 9, 10, and it is going to be a bear to cast.
My thought is that you should find a better place to cast to these fish.
Genetic pollution damages wild
stocks, bonk those Hatchery Zombies!