Čertovo jezero, Glacial lake in Železná Ruda, Czech Republic.

Čertovo jezero is a glacial lake in the Šumava region situated at roughly 1,030 meters elevation, spanning several hectares with depths reaching about 37 meters. The water sits between steep, forested banks typical of high mountain lakes, with a cool, dark surface reflecting the surrounding terrain.

The lake formed during the Würm glaciation, when glacial ice carved the hollow on the southeastern slope of Jezerní hora. In 1911 the landowner Vilém Hohenzollern, prompted by the German botanist Dr. Hugo Konwentz, had the area of this lake and nearby Černé jezero protected; in 1933 both became part of a national nature reserve. A steep Lávková cesta once ran above the lake and is now closed.

The name Čertovo jezero means Devil's Lake. German sources record a legend that between this lake and the Černé jezero 1.5 km to the northwest, Carl Maria von Weber's Der Freischütz cast his magic bullets. The two lakes are separated by the European watershed.

The lake is accessible via marked hiking trails starting from nearby towns, with route conditions varying by season. Visitors should prepare for steep sections and bring weatherproof clothing, as the high elevation means conditions can change quickly.

Between Čertovo jezero and Černé jezero, 1.5 km to the northwest, runs the European watershed; the lake is the most humic-acid-rich in the Bohemian Forest. Legend says Carl Maria von Weber cast his magic bullets for Der Freischütz in the wild between the two lakes.