In the present study, the author has assessed drought streamflow deficits, and the characteristics of the low flows at a constant and variable (monthly) low-flow threshold. The low-flow truncation level was identified based on the 70th percentile from the flow duration curve (Q_70%). The flow at ordinate 95% was assumed to be the threshold for the deep low-flow. Thirteen catchments in the Vistula basin, varying in size, river regime, and physico-geographical conditions, were selected for the study. The input data was series of daily discharge from the period 1951–2016, made available by IMGW-PIB (Polish Institute of Meteorology and Water Management – National Research Institute). Analyses were conducted for drought streamflow deficit volume in absolute and relative values, low-flow duration and deficits contributing to severe low-flows were calculated for temporal scales of months and years. Comparison of the obtained results led to the determination of the basic factors affecting the formation of drought streamflow deficits, and the indication of restrictions when applying fixed and variable criteria for identifying river low-flows.