This report presents the results of a preliminary evaluation of possible solutions to reduce flood damages from Willow Creek to Mason City, Iowa. The purpose of the Reconnaissance phase is to make a determination whether the planning should proceed further based on a preliminary appraisal of the Federal interest, and if potential solutions are in concert with current policies and budgetary priorities. The city of Mason City is located in Cerro Gordo County in north-central Iowa. Willow Creek flows generally easterly through Mason City and joins the Winnebago River just upstream from Kentucky Avenue (see plate 1). This study evaluates possible solutions to reduce flood damages to the Mason City community. This study was initiated in June 1988 when representatives from Mason City and the Rock Island District met and reviewed the flood problems associated with Willow Creek. The Rock Island District received funding for the reconnaissance study in August 1988. This report presents the results of engineering, economic, and environmental investigations. These investigations are in sufficient detail to determine if any potential solutions will likely have Federal interest. (sdw).