I'm sorry, but there seems to be some confusion with your prompt. The Whitewater River and Horseshoe Lake are located in Minnesota, not Iowa. Additionally, the BWCAW (Boundary Waters Canoe Area Wilderness) is a protected wilderness area located in northern Minnesota and does not border Iowa. Assuming you intended to ask about the Whitewater River and Horseshoe Lake in Minnesota, the ideal streamflow range for the Whitewater River is typically between 150-500 cfs. The river is classified as a class I-II, meaning it is suitable for beginners and intermediate paddlers. The segment mileage varies depending on the put-in and take-out locations, but the most popular run is approximately 7 miles long. The most notable rapids and obstacles on the Whitewater River include the Class II "Big Drop" and "Triple Drop" rapids. Horseshoe Lake, located at the beginning of the run, offers calm paddling and scenic views. Specific regulations for the area include obtaining a permit for overnight camping in the nearby Whitewater State Park and following Leave No Trace principles. Additionally, motorized boats are not allowed on Horseshoe Lake.