Little Eau Pleine - old RR right-of-way off Marsh Road to Mann/River Rd (9.3 or 3.4 mi) (WI)
Likely less than 50 cfs: almost certainly too low for reasonable whitewater run.
For those wanting the shortest trip, with just the best action (the dells is just a short bit downstream), Hwy.97 makes a good put-in.
USGS lists a sampling site here with drainage area of 78 square miles.