Preliminary evaluation of submersed macrophyte changes in UMR Rogers, S. J. 1994. Preliminary evaluation of submersed macrophyte changes in the Upper Mississippi River. Lake and Reservoir Management 10(1):35-38. Reprinted by the National Biological Service, Environmental Management Technical Center, Onalaska, Wisconsin, June 1996. LTRMP 96-R007. 4 pp. ABSTRACT Declines in submersed aquatic macrophytes, notably Vallisneria americana Michx., recently have been observed in portions of the Upper Mississippi River (UMR). Coincidentally, Myriophyllum spicatum L. appears to have become more common, frequently occurring in locations formerly occupied by Vallisneria or other submersed aquatic species. Mechanisms causing these changes in the abundance and composition of aquatic vegetation are unknown. However, a 3-year drought may have affected nutrient transport and phytoplankton production, thereby influencing growth and reproduction of Vallisneria and other macrophyte species. Other factors may potentially affect populations of submersed macrophytes within the UMR. Foremost among these are suspended sediment concentrations, flooding, herbicides, and grazing. KEYWORDS aquatic plants, invasions, Myriophyllum, plant management, Vallisneria