Plešné jezero, Glacial lake at 1090 meters in Nová Pec, Czech Republic

Plešné jezero is a glacial lake at 1090 meters elevation in Nová Pec that spans approximately 7.5 hectares with a maximum depth of around 18 meters. The water sits in a basin carved by ancient ice, surrounded by rocky slopes and forest on most sides.

The lake formed in a cirque carved by a slope glacier during the Quaternary; its front moraine, 30–40 m high, dammed the water. In 1789–1793 the moraine was sealed and a 2.5 m dam with sluices was built to regulate outflow for floating timber in the Schwarzenberg Canal, allowing up to 177,000 m³ to be released.

On the rocky wall above the northwestern shore stands a granite obelisk erected in 1877 to Adalbert Stifter, who set his novella Der Hochwald at this lake and also mentioned it in Granit. A trail from the water, the Duch pralesa nature path, leads up to the monument.

The lake is open on foot year-round. Marked trails lead from Nová Pec (7 km, green), Černý Kříž (13 km, yellow/blue/green), Nové Údolí (16.5 km, red/yellow) and Přední Zvonková (19 km, red/yellow); cycle route 1029 comes from Stožec (13 km). The Stifter monument above the northwest shore is reached by the Duch pralesa nature trail.

The lake holds two Czech endemics: the quillwort Isoëtes echinospora and the copepod Heterocope saliens. The 1935 measurements also found the outflow too weak to power even a small turbine for the lakeside hut without cutting the water supply to the Schwarzenberg Canal.