The paper describes the design and construction of the Włocławek water barrage operating on Vistula River for more than 50 years. The construction of the barrage and the damming up of the Vistula River caused changes in the hydraulic and thermal regime of a fifty-kilometre long stretch of the Vistula River, resulting in some ecological changes as well. Some ecologists consider these changes as eminently unfavourable and call for the dismantling of the barrage, but not all experts are of the same opinion as the construction may be regarded as a important technical, economic and social achievement, primarily because of the electricity produced, which is renewable and ecologically clean.