Many of already existing roads cross wetland river valleys. Also the roads nowadays planned are cutting through valuable wetlands. It is necessary to evaluate the range of their impact on the natural environment. This paper focuses only on the analysis of the road crossing impact on the groundwater level. Two options of crossing the wetlands were analyzed, building the road on embankments and in the bridge. It was assumed that the valley is filled with organic material under laid by permeable sands. Calculation results showed that building a road in the valley affects groundwater level only to the slight extend. Water conditions in the valley may be affected only during the construction of the road. Calculation results were confirmed by field observations.

It should be stressed that the object of this paper is the evaluation of water conditions. Environment might be influenced by other factors.

The aim of the study was to determine the extent to which created and functioning beaver dams contribute to increasing water retention in the Łąki Soleckie facility (Mała River valley). Changes in the plant cover of meadow habitats within the range of beaver dams were also determined. During the growing periods in 2020–2022, measurements of the periodic levels and water retention of the Mała River and the adjacent ditches (R-27, R-29) were closely related to the activity of beavers and precipitation. The maximum volume of water retained in the Mała riverbed in 2020–2022 was 1,300, 1,700, and 1,200 m³; the maximum retention of the R-29 ditch was 270, 210, and 200 m³, respectively. In 2021–2022, the R-27 ditch collected the most water – 270 m³and 250 m³. Starting from June 2022, due to beaver dams D2 and D3, the water level in the river and water retention have stabilised at a high level, despite slight rainfall. The activity of beavers contributed to the transformation of communities of wet habitats located on organic soils (Calthion) into communities of periodically wet habitats (Caricetum gracilis). In places where natural habitat 6510 occurs, the coverage of species of the Festuca genus has increased, and the value of the biodiversity index has increased by an average of 9%. High stability in the community of expansive species (Deschampsia caespitosa and Veronica longifolia) and their increasing cover may make it difficult to maintain the proper condition of natural habitat 6510.