Forggensee, Artificial lake in Ostallgäu, Germany

Forggensee is a reservoir on the Lech north of Füssen in Ostallgäu, Bavaria, with a surface area of 15.2 km². It extends about ten kilometres north to the dam at Roßhaupten, reaching a width of one to two kilometres. The photograph shows bright blue water narrowing to a pale turquoise arm, a sandy spit on the right bank, and red-roofed houses among green fields in the lower left.

Plans for a reservoir at Roßhaupten date to 1898, when Siemens & Halske bought land and obtained a licence that lapsed in 1907. After war delays, BAWAG began the dam in 1951; the 1952 Schwangau Agreement settled resettlements. The reservoir submerged the hamlet of Forggen, whose ruins reappear when the water is drawn down in winter.

The name comes from a hamlet that disappeared beneath the water. Today the reservoir supports power generation and flood control while remaining open for leisure activities.

The water level changes considerably, especially in winter when it drops by several meters. Best access is through shore roads in the area, where parking and boat launch points are available.

When the level drops in winter, old Roman traces and remains of Stone Age hunting camps reappear. These finds show that the valley was inhabited thousands of years ago.