Both.  Kinda on the bottom with a few split shot.  Had 2 vicious strikes using a float(probably hybrids I'm gussing as I let it drift to where the water shoots out of the sluce which is where I usually catch them), but had too much slack line out and couldn't set the hook.  Just make sure you keep your minnows alive, and you'll catch at least something.  If they die you still might get a cat, but they still prefer them alive. 

How deeP is it right by the dam?

I honestly have know idea.  Always wondered that too.  It's pretty deep I'm guessing, but then it gets extremely shallow.  Very easily waded, and you can wade across the entire river with maybe max 3 gates open(I've never tried crossing it any higher levels,  but you might at 4 not sure).  You'll spook a handful of carp in the shallow riffles, thats where I targeted them fly fishing, from the dam until it gets deeper a little farther downstream. 

I was just curious cuz I'm going to start out fishing right by the dam and wondered how deep to rig my slip float

How was the water level today?

I usually have my float maybe 3 feet above my bait, sometimes 4, but never really measured it.  I do like using slip floats there, but I find my self using the ones with the springs on them more since you can take them off without having to take apart your whole rig.  I think just freelineing it with a few split shot is more effective, but thats just my opinion.
 
There was only 1 gate open, so it's the lowest it will get.  I don't see that changing by tomorrow.  For fishing below the dam I found 2, 3, or 4 gates open to be better, but believe it or not my best ever day there(about 20-30 walleye and white bass with some other stuff mixed in) there was only 1 gate open.  For fishing downstream areas though I found just 1 and sometimes 2 gates open to be ideal.  

Hehe, here's one of the many decent hybrids in there, and I used a slip float(as you can see in the pic). IMO though I still think fishing floatless is more productive fishing off the wall, but wading I almost always use floats because of snags.
 
 

To fish rigt by the dam do you have to fish off the wall?

If you're around tomorrow and have time you should stop by. I'll be the guy with way to much gear wearing a cutoff with some tattoos. And I'll have a red cooler with me

Attached is a pic of what it looks like(oh and it's not normally that crowded, in fact my brother and I had the whole place to ourselves today).  You can either fish off one of the walls or wade.  Fishing off the wall gives you access to deeper water I guess, and I seem to get most of my hybrids off of the walls, but I still catch tons of fish(of all kinds) wading.  So just whatever you prefer. The only disadvantage to fishing off the wall is if you hook into a bigger fish you have to walk it down, and there's usually other people you have to deal with, so if I see people on the walls I usually wade.  Usually there's people at the wall on the parking lot side of the river(not pictured), but I usually wade across and fish the opposite wall which usually has nobody on it.  Again though wading can be just as productive. 
 
I highly doubt I'll be able to fish tomorrow, that's why I went today, but if I do I'll stop by.  Good Luck