There are definitely some big blue cats there. Try around March/April during the shad run up the river to the dam. The cats will sit under the large schools waiting for a meal.
If you are fishing from a boat, don't use a good anchor as there is a lot of junk on the bottom and you will probably get snagged. Lots of guys use a cinder block with a section of heavy duty mono between the block and the main line. that way if the cinder clock gets hung it will break off and you aren't out an anchor.
Blues will keep biting in the cold weather as well. They don't slow down like Flatheads and Channels do. They just won't be as aggresive as they are when the shad are schooling. Bottom fishing with cut bait,liver works well.
Definantly big cats in the river. I use eels and small bream hooked on a carolina rig cast out in the middle where the tubulence calms a little. Liver and cut bait are also good choices. Got to be careful up close to the dam more than a few boats have sunk form people getting to close and careless.