Water Quality of the Doa Stream in Gliwice (Southern Poland) in the Context of the Functioning of the New Dry Retention Reservoir

Maintaining the appropriate quality of surface waters in urban areas is one of the significant environmental problems. Failure to monitor the chemical and quantitative status and control industrial facilities may lead to environmental and human health hazards. The Doa stream catchment area is one of the last natural areas in Gliwice (southern Poland), which makes it the subject of a conflict between the need to build flood protection infrastructure and environmental protection. During the annual studies of changes in the quality of surface waters in the Doa stream, a clear seasonality of physicochemical parameters was observed, resulting from both natural annual cycles and anthropogenic impacts. The calculated Nemerow indices reach almost 18 in the spring months and about 25 in the winter months, which classifies the water quality in this stream as the V quality level. Additionally, the differences between the electrical conductivity value at individual measurement points indicate a deterioration in the quality of the stream after flowing through the retention reservoir. For this area, a detailed environmental inventory of the catchment area, regular monitoring of the reservoir’s effectiveness in terms of reducing flood risk and improving rainwater retention, and an assessment of whether the reservoir causes any negative impact on local ecosystems, particularly in the context of hydrological changes, water quality and biodiversity, are suggested.