I can only advise as to what works down here, South. I usually go behind the spillway and tailraces. I use an 9-1/2' 8 wt. rod with a butt extension, with a Shooting Head and line (like for Tarpon and Bonefish) and a 6' 2X or 1X tippet. You don't need long tippets because catfish are not particularly line-shy.
I used to use a size 6 black clouser-style minnow, tied with ostritch herl instead of bucktail. But I have since made my own fly (I think) that resembles a shad. It's sort of like a Polor Minnow, but I use Angel Hair, or Puglisi Fibers, or whatever is on sale. I weight it with wire on the hook shank. I think any minnow imitaion that mimics the local forage fish will work. Crawfish patterns should work as well.
I fish in the evening, night or early morning before daylight. Double-Haul casting is very helpful here. I spray my fly very liberally with either Shad or Baitfish Smelly Jelly (whichever is appropriate), and cast upstream towards the turbines/locks. I allow it to drift, twitching it frequently to imitate a wounded fish just comming through the machinery. About every other drift, I will usually nail a cat, or sometimes a striper. Either way, it's pretty much 'hang on and pray'! They hit viciously and fast.
Here is the fun part. You must be able to move downstream when necesary. You cannot let the fish get downstream of you, because you can't pull against the weight of the fish and the current without damaging your rod and/or tippet. Usually, if you exert pressure to the upstream side, the fish will turn that way and stay upstream of you. You need to maneuver the fish to the shore where you can beach it, or net it. That's all there is to it. It's sort of like flats fishing on a budget!
One safety tip: You need to pay close attention to the sounds of the water. Some places open the gates with no warning. The sound level will go up, and next thing you know, you're knee-deep in fast water! Be prepared to move quickly.
If you go in, do not try to fight the current. ( I am an expert at this) Just ride it until you can get out. Almost every spillway I have ever seen has shoals 1/8-1/4 mile downstream where you can pull yourself out. I have been dunked over a dozen times, and have never even lost my fly rod, or fish. If worse comes to worse though, lose the rod as a last resort. You can always buy another rod, but if you drown, your loved ones are going to be real mad at you.
The same techniques work for freshwater stripers. Just go in the daytime. I usually catch a mixture of both.
This is probably not for everyone. It is very intense living in a short time period.
Next month, I am going Shark-Fishing with my fly rod from my Kayak down in Fla. That's gonna be fun! I'll submit a report and pictures when I get back.
Semper Fi!