Drought Drains Orlík Reservoir by 15 Metres — For the First Time, Slapy Is Replenishing Two Rivers at Once

The Vltava cascade of reservoirs is going through a tough season due to a prolonged drought: the water level at the Orlík reservoir has dropped by 15 metres, reaching 334.6 metres above sea level, compared to its usual 350 metres. According to Povodí Vltavy, the water management company overseeing the cascade, water stored in the Slapy reservoir is being used for the first time in history to maintain flow in two rivers simultaneously — the Vltava and the Elbe.

As Povodí Vltavy spokesperson Mertlová explained, the main purpose of the Vltava cascade is precisely to compensate for water shortages downstream during periods of drought. The Vrané weir currently releases a constant 40 cubic metres of water per second — a volume needed to dilute treated wastewater, supply water intake points, and sustain the aquatic ecosystem. Without this replenishment from Orlík and Slapy, the flow of the Vltava near Prague would currently amount to just 10–15 cubic metres per second.

Reserves Should Last Several More Months

Despite the falling water levels, Orlík and Slapy together still hold 47% of their usual volume and can continue feeding the rivers for several more months even without rainfall. The cascade was designed precisely for such weather swings: it holds back water during floods and, conversely, sustains river flow during droughts.

Back in February and March this year, the reservoirs were actively accumulating water, and Orlík was filled to 94% of capacity. But since April 10, the Vrané weir has maintained a minimum release of 40 cubic metres per second, meaning more water has been flowing out than coming in ever since — and reservoir levels have been gradually dropping. A lack of rainfall combined with increased evaporation from the heat has only made matters worse.

Trouble for Boat Owners and the Nuclear Plant

The falling water level at the Slapy reservoir (currently 269.3 metres above sea level) will directly affect boat owners. The free ferry service run by Povodí Vltavy will only be available as long as the water level stays above 268.5 metres — once it drops below that mark, the water authority will halt boat transport for safety reasons. Registration for the ferry crossing remains open at pvl.cz until Sunday.

At the end of the cascade lies the Lipno reservoir, a popular holiday destination that also serves an important technical function — it supplies water to the Hněvkovice reservoir, which in turn provides cooling water to the Temelín nuclear power plant. Lipno is maintaining a minimum release of 6 cubic metres per second, while inflow currently stands at just 1–2 cubic metres per second, causing the reservoir to gradually shrink as well. Its level currently stands at 722.16 metres, compared to a normal level of 724.9 metres. However, Temelín will not need to reduce output — thanks to its cooling towers, the plant uses significantly less water than power stations relying on direct river cooling.

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Around Prague, based on reporting by novinky.cz