Changes in species composition and plant cover were studied in relation to moisture regime over a 10-year period in 71 shallow marsh wetlands in the grassland and parkland regions of Saskatchewan. Decreases in density of the shallow marsh emergents Polygonum coccineum, Carex atherodes, Scolochloa festucacea, and Eleocliaris palustris occurred with greater-than-normal water depth at the start of the growing season but 2 or more years of continuous flooding were required to eliminate emergent cover completely and convert the wetland to open water. Repeated autumn reflooding also resulted in complete elimination of emergent species. Changes in species composition occurred when basins were grazed and as vegetation reestablished after cultivation but no changes followed mowing or burning. Alopecurus aequalis, Beckmannia syzigachne, Glyceria grandis, and G. pulchella are designated as "disturbance" species on the basis of their response to soil-exposing events. Presence of small amounts of deep marsh emergents in shallow marsh wetlands is not considered a reliable indicator of wetter moisture regime. Species composition of rooted submergents in a wetland can be used as an indicator of its moisture regime. Shallow marsh wetlands in basins of 1 ac (0.41 ha) or less experienced little year-long flooding and converted to open water only under atypical conditions. Larger wetlands required basin depths in excess of 36 in. (96.4 cm) to have any amount of year-long flooding and to convert to open water. These basin size and depth criteria have applications in habitat evaluation by waterfowl managers.