This thesis presents Lešće hydroelectric power plant, an impoundment facility with a barrage power station, located on the River Dobra whose river basin is well-known for its natural beauty and numerous plant and animal communities. The aim is to introduce the implemented alternative design solution as well as to analyse possible environmental impacts resulting from the construction of the hydroelectric power plant. Since the thesis is conceived as an environmental impact study, most key elements of any environmental impact assessment are discussed. After explaining the legal framework, i.e. the relevant articles of the Environmental Protection Act and the obligatory procedures involved in an environmental impact assessment, the location of Lešće hydroelectric power plant is presented, focusing on its geological, hydrological and climate features as well as the typical plant and animal communities. The next chapter deals with the project itself. The considered alternative design options are described, and a more detailed description of the implemented alternative design solution is given. Potential environmental impacts are defined and the elements of the environment which could be affected by the construction of the hydroelectric power plant and should be protected in accordance with the Act on the Environmental Protection, are analysed. Based on the analysis, it is concluded that Lešće hydroelelctric power plant has a considerable environmental impact, especially on the soil, water and animal ecosystems. The operating conditions of Lešće hydroelectric power plant cause the natural hydrological regime to change. In addition, they create favourable conditions for the river bank erosion downstream of the dam as well as for water wave formation. The modified conditions also affect numerous fish communities and tourism activities in the area, especially downstream of the dam. Finally, different measures already taken in order to reduce the environmental impacts as well as the future actions, that were only under consideration at the time this thesis writing was still in progress, are listed and discussed.