Soboth Reservoir, Reservoir in the tri-border area of Carinthia, Slovenia and Styria, Austria

Soboth Reservoir is an artificial lake on the Koralpe, created in 1990 by an embankment dam on the Feistritz stream. It lies at about 1080 m above sea level, roughly half in Carinthia and half in Styria, near the Soboth Pass and the Slovenian border. It is around 2.6 km long, up to 970 m wide, covers 0.8 km² and reaches 80 m deep, holding some 23 million cubic metres of water.

The Koralpe power plant was built between 1987 and 1991 as a passive storage station, and the reservoir was created in 1990 when an embankment dam on the Feistritz stream was completed. Between 2009 and 2011 the plant was expanded into a pumped-storage station, adding an upper basin function. During dam construction the old bridge over the Feistritz was blown up, and its debris remains underwater.

The reservoir takes its name from the village of Soboth on the Lavamünd–Graz road, near the Soboth Pass by the Slovenian border. Since the 2010s it has also served as the upper basin of a pumped-storage plant. A nature-protection condition keeps the water level within one metre between 15 June and 31 October, which underpins its use for swimming.

The area around the lake has well-maintained paths, toilets, bars, and spaces for sunbathing and picnicking, plus a camping site for tents and caravans. Parking areas are marked and charge fees from early morning until early evening, with yearly passes or hourly rates available.

Every ten years the reservoir is fully drained for maintenance, and the remains of a bridge over the Feistritz, blown up when the dam was built, reappear along with other submerged structures. The drawdown is scheduled in winter so the lake can hold its level for swimming from mid-June to the end of October.