In 1990, vegetation distribution and abundance were studied along five belt transects in Pool 13 of the Upper Mississippi River as part of the Long Term Resource Monitoring Program, with 162 individual site plots sampled on five transects. Using quantitative sampling techniques, 72 plant species were identified. Floodplain forest communities exhibited the highest species diversity, with 61 species represented. Shallow open water communities exhibited the lowest species diversity, with three species represented. Species richness in aquatic habitats was significantly less than in terrestrial habitats. Of the 72 taxa cataloged in 1990 sampling, Acer saccharinum, Vitis riparia, Toxicodendron radicans, and Laportea canadensis were the dominant tree, shrub, vine, and ground layer species in floodplain forest communities. Cephalanthus occidentalis and Leersia oryzoides were the dominant shrub and ground layer species in wet meadow communities. In shallow marsh communities, Sagittaria latifolia, Nelumbo lutea, and Lemna minor were the dominant emergent, rooted floating, and non-rooted floating species present. Nelumbo lutea, Ceratophyllum demersum, Lemna minor, and Wolffia columbiana were the dominant emergent, submergent, and floating species in deep marsh communities. In shallow open water communities, non-rooted Myriophyllum spicatum, Ceratophyllum demersum, and Lemna minor were the dominant submergent and non-rooted floating species. A large number of floodplain forest communities was observed in the upper pool. This number was greatly reduced in the lower pool, where open water communities prevail. The highest species richness was observed in the Running Slough transect, which was characterized by many habitats such as narrow islands and sloughs. The lowest numbers of both terrestrial and aquatic species were observed on transects in the lower pool, which consisted primarily of large expanses of open water.