The preparation of the construction began already during the Second World War, when the most suitable place for the dam was selected. It was also decided to build a dam with a hydroelectric power station with a spillway. This resulted in a solution with a power plant located directly in the dam body under the spillways, which was almost unique in Europe at that time. In 1949-1951, a bypass tunnel was broken out in the rock on the right bank. It is horseshoe-shaped with a profile area of 100 m2 and is 360 m long. After the construction of the dam was completed and before it was filled in 1954, it was closed. The closure consists of a 300-tonne reinforced concrete box. The lower part of the tunnel up to the concrete seal is still accessible by boat. In 1952, preparatory construction work on the dam began. These included the construction of cable cars, concrete plants, roads, etc. Three cable cars were built, one transporting aggregate from the quarry in Teletín, the second from Štěchovice gravel and the third from Luka pod Medníkem cement station. Thus, the material for the production of 374,320 m3 of concrete was transported and used for the body of the dam. The construction was completed in 1955, including the commissioning of the plant for trial operation. Even before the flooding, some monumental objects were identified and moved across the flood line of the reservoir. These were rather small buildings, the most important of which is probably the column and statue of St. John of Nepomuk, standing today in the hillside below the Slap Dam.
The Slapská Dam is a straight, heavy concrete dam, founded on solid bedrock. The crown is 260 m long and 67.5 m high above the foundation. The crown spillway consists of four fields with a clear width of 15 m. Another device is two lower outlets, which are used for the eventual draining of the reservoir. They consist of a 4 m diameter steel pipe and are located in the middle of the two outermost blocks. There are 6 inspection passages in the dam. The lake is 44 km long with a surface area of almost 14 km2 and a volume of 269,3 million m3.