Clay Hole is a popular whitewater play spot in Iowa.  It is located in Cedar Falls.  There is a city park right next to the rapids where you can park and steps leading most the way down to the put-in spot.  Watch you footing on the rocks and boulders that is lining the river shore it is an easy way to hurt yourself.  This rapid is created by an old dam that has been destroyed.  The remnants of the dam is what creates the nice wave to surf on.  This may be best wave to surf and to do tricks in Iowa, at this time.