hey nepeg - here is a IDNR document from March 06' talking about the status of the fishery.
Illinois River is page 10.
From what I understand, the fish go upstream in the spring to spawn and once they spawn head back downstream, so I would guess that if everything comes together (water level, temp, time of year) they would go into the next pool if they can make it past the dam, but if it's getting too close to spawn time, and conditions are not right, they congregate at the dam and spawn there. I've also read some material from other States that the fry tend to drift downstream after hatching, so there could be a two way exchange in effect. There are sauger in the Morris pool, and a there has to be a pretty good native population, but I wonder if any migrants may actually be from the K3 or DesPlaines. Iím sure itís a mix from everywhere, but you donít see the Asian Carp in the Morris pool like you do around SR or even Ottawa, and there has to be a reason. I don't claim to know anything about this, just some ideas I put together after some research, so please don't take offense if you disagree.
Also, check your pm nepeg