Lipno Reservoir

The Lipno Reservoir, sometimes called the “South Bohemian Sea,” is the largest reservoir in the Czech Republic, covering 48.7 km². The reservoir stretches 42 km in length, with a maximum width of 5 km. While most of the reservoir is relatively shallow (average depth 6.6 m), the section from Frymburk to the dam reaches a maximum depth of 25 m, resembling steep canyon-like reservoirs.

Built between 1952 and 1959, the reservoir serves multiple functions, including:

• Flood protection
• Hydropower generation
• Recreational activities, water sports, and fishing

The hydroelectric plant, operating in a peak-load mode, is a unique engineering structure situated 160 meters underground. The cavern housing the power station measures 65 × 22 × 37 m and can be accessed via a 200 m inclined tunnel. The space is so vast that it could allegedly fit the entire nave of St. Vitus Cathedral in Prague (the largest cathedral in the country). Guided tours (approx. 1.5 hours) allow visitors to see turbines, generators, and a 3-km-long discharge tunnel. Participation is restricted to pre-registered visitors aged 15 and above, with group sizes limited to six.

In recent years, water quality in the Lipno Reservoir has become a widely discussed issue. Our observations indicate that the reservoir fails to meet the EU Water Framework Directive’s criteria for good ecological potential. Cyanobacteria constitute nearly 50% of total phytoplankton biomass annually, rising to 70% in summer, leading to frequent cyanobacterial blooms across multiple locations. This eutrophication is primarily driven by excessive phosphorus loading from municipal wastewater.