Water level data have been collected since 1968 for small wetlands within a 385 ha area in the northern prairie region of Canada. The uplands around the wetlands were under dryland cultivation prior to 1968 and there was no significant change of land use until 1980. Between 1980 and 1983 about one-third of the area was converted to a permanent undisturbed cover of smooth brome grass (Bromus inermis) and some alfalfa (Medicago saliva) with the purpose of providing improved bird nesting habitat. The remainder of the area continued in cultivation. Wetlands within the grassed area dried out within a few years after conversion of their catchments to permanent brome grass, whereas wetlands in the neighbouring cultivated area retained water as before. Within the area of permanent grass cover springtime snowmelt runoff essentially ceased. These observations demonstrate that the water balance of prairie wetlands is very sensitive to the land use on the surrounding uplands.