Discussion in this paper concerns the elevation of water surface along Warsaw’s Vistula River section on the base of field measurements. They have allowed to create a model of this section of river for steady flow in HEC-RAS software (version 4.0.1), whereby simulations were performed for different flow conditions. On the basis of simulations’ results an attempt to determine the significance of Reef in Żoliborz for the downtown section of the Vistula River in Warsaw was made. The analysis showed that it is an important element in the longitudinal profile of the river and impacts water surface level along Warsaw’s Vistula River.