I’ve fished the Niobrara at the Spencer dam by O’Neill. Pretty muddy there, the kind of place where you can catch a lot of fish, but usually nothing special. It gets prettier as you go west to Valentine. The Snake out there is good trout fishing, but tough access.
The Missouri above Lewis & Clark is a bass, walleye, pike, catfish, crappie mecca. It’s a very alluring place. At times, especially in the winter, you can see down 10′ believe it or not.
I’ve had days where I’ve caught 25 18″ smallies, and I pretty much stink as a river fisherman for bass. There are largemouth too, harder to find, sorta seem to max out at 5# for me. Sometimes it takes a 4-5# avg to win a tourney – w/smallies!