Pretty much every river in SE Minnesota and NE Iowa is loaded with smallies. These are all pretty small rivers and boat access is pretty much nil, save a few that are large enough for a canoe.
The keys for me on these smaller rivers are rocks/rip-rap, current, and a little extra depth nearby has never hurt. I would suggest following JonJ’s advice – 1/16 to 1/8 jigs with a white twister swam over and around the rocks (current breaks). Rattletraps and small spinnerbaits work for more agressive fish, but it’s hard to get a spinnerbait to run true in heavy current.
Don’t forget that smallies are a very current tolerant fish, and they’ll hold in current that’s too fast to safely wade if they can find a break to rest in. Don’t be afraid to cast in there and give it a shot.