Recreational boating impact investigations Johnson, S. 1994. Recreational boating impact investigations - Upper Mississippi River System, Pool 4, Red Wing, Minnesota. Report by the Minnesota Department of Natural Resources, Lake City, Minnesota, for the National Biological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, February 1994. EMTC 94-S004. 48 pp. + appendixes (2 pp.). (NTIS # PB94-157906) ABSTRACT Field investigations were undertaken to document physical and water quality impacts associated with recreational boating activities in upper Pool 4 of the Upper Mississippi River System. The study documented high erosion rates irrespective of geomorphic position in the Main Channel and development of a diurnal turbidity plume in the littoral zone. A comparison of commercial tow, wind, and recreational boat surface wave characteristics, along with other observations and the use of a control channel provided the perspective necessary to determine relative responsibility for the observed impacts. Recreational boating was found to be the contributing influence most responsible for the high shoreline erosion rates documented along the Main Channel and was found to be directly responsible for the development of the diurnal turbidity plume in the Main Channel's littoral zone on weekends and holidays. Other applicable literature findings were reviewed and potential impacts to the river habitat and biota associated with recreational boating activity were identified. Federal, State, and local government agencies responsible for managing the Upper Mississippi River System should respond to the findings of this report by implementing programs to protect the river from recreational boating impacts. KEYWORDS Upper Mississippi River, recreational boating, shoreline erosion, water quality, surface waves, contributing influences, geomorphology