The paper concerns the transformation of water resources induced by the construction and functioning of the Brest Fortress defence structure and presents the current water resources resulting from these changes. The study was conducted by analysing historical materials: maps, plans and written documents. Hydrographic changes were analysed for five study periods covering almost 200 years, from 1823, presenting the hydrographic network before the construction of fortifications, up to 2018, when most of these structures ceased or were repurposed. Hydrographic changes were analysed in detail for the area of the Terespol Fortification. The analysis revealed that almost 80% of the wetland area had disappeared after intensive drainage works, and several dozen originally small and isolated areas had been incorporated into a vast drainage network. One of the consequences of these activities was the creation of significantly transformed artificial catchments within the study area.