The role of the effects of salinity and different hydrological regimes on growth in Groenlandia densa (Potamogetonaceae) was investigated under laboratory conditions. The experiment consisted of three treatments of hydrological regimes (severe, moderate and well watered) and five levels of salinity (0, 125, 250, 375 and 500 mol.m(-3) which are equivalent to 0, 25, 50, 75 and 100 % sea water salinity). Survival, lengths of shoots and roots and dry matter production were measured. Our results suggested that the growth of roots was significantly reduced at salinity of 250 mol m(-3) and significantly enhanced at 500 mol m(-3) compared to a freshwater control. Both salinity and water deficiency significantly impacted root and shoot dry weights. Plants exhibited maximum reduction in dry mass production in response to increasing salt stress. Additionally, leaf chlorosis occurred in plants under increased salinity and water deficiency conditions which may be related to the adverse effects of salinity on plant nutrient status. In this study, a simple model was created according to data from the literature. The model suggested that crowding is an important factor in limiting G.densa growth.