Floodplain shallow aquatic areas contain a mosaic of open water and emergent vegetation interspersed among islands. The boundaries of these areas are defined by the apparent shorelines and by other aquatic areas. Boundaries of floodplain shallow aquatic areas are often irregular. Where floodplain shallow aquatic areas grade into impounded areas, the boundaries will be lines connecting the downstream points of islands or peninsulas across the floodplain. The downstream boundaries of impounded areas are the navigation dam and connecting dikes.
Landward boundaries are the apparent shorelines or the boundaries of other aquatic areas.
Upstream boundaries are with islands and floodplain shallow aquatic zones. Riverward boundaries are channel border zones. Boundaries are the apparent shorelines. The downstream boundary for contiguous abandoned channel lakes is a line that is a continuation of the apparent shoreline of the lake. Abandoned channel lakes vary greatly in size.