 The main European water divide runs across the mountain just above the lake.As a consequence, Černé jezero belongs to the water basin of the Elbe, which finds the North Sea, while Čertovo jezero just 2 km away drains into the Danube and thence the Black Sea.The oldest pumped-storage hydroelectric plant in the Czech Republic (built 1929-1930) is located here; the lake serves as its upper reservoir.