I’ve fished it more around Central City, Quasky, and Independence, and Littleton. Lots of smallish bass around Quasky and Littleton dams, I’ve had brief ‘fish every cast’ episodes in both places, but all 12″ or smaller. CC and Quasky have both generated 18+ fish in the past around the dams, and some big fish in the slower parts of the river in between Troy and CC in the wood during mid-late summer.
I tend to do just as well or better on smallies in the Maquoketa, but oddly not in the catch & release area. One day I caught four smb’s bigger than 18″ at the Manchester dam, with fish coming above, below, and right in the pools of the dam.
As far as Northerns go, a lot of people fish for them around Troy, but I’ve never really targeted them that for down the river. A couple years ago the DNR fishing report claimed lots of walleyes were caught in that section as well, but I didn’t investigate too heavily. The last I heard, the Wapsi was the only internal Iowa river that had a self-sustaining population of pike.