The Slapy reservoir is a part of the Vltava Cascade, a system of nine reservoirs together retaining 1.4 billion m3 of water. The dam of the Slapy reservoir was constructed at the 91.7 km of the Vltava River in 1949–1954 and the reservoir impounded in 1955. The dam is 60 m high and 260 m long. Reservoir volume is 270×106 m3. Just below the Slapy dam, there is the end of impoundment of the small Štěchovice reservoir (built earlier in 1938–1944). Only several small brooks enter the impoundment of the Slapy reservoir, the mean yearly flow through the Slapy reservoir is 83.8 m3 s-1 and the mean hydraulic retention time is 38.5 days. A large Lipno reservoir in the upper part of the Vltava River was built in 1952–1959. In 1961, another part of the Vltava Cascade, large Orlík reservoir was built above the Slapy reservoir and later several small reservoirs. The total catchment area of the Slapy reservoir is 12 968 km2.

The Slapy reservoir is a canyon shaped water body mostly with steep banks. An electric power station, working in peak hours (morning and evening), is located in the dam. As a consequence, periodic seiches occurred, water level fluctuates, and a littoral zone with aquatic plants is not developed. The reservoir is intensely used for recreation and locally as a drinking water source.

Regular investigations include major physical and chemical characteristics and pelagic biota (bacteria, protists, phytoplankton and zooplankton). The sampling point is located 8.8 km downstream of the dam in a lacustrine zone of the reservoir. Long-term research in the reservoir already yielded valuable results explaining long-term effects of anthropogenic and land use changes in the catchment, such as the construction of the upstream reservoir, agricultural practice (e.g. drainage, changes in arable land area and fertilization rate), wastewater treatment, road de-icing etc., on water chemistry and biology.