Altmühlsee, Reservoir in Weißenburg-Gunzenhausen district, Germany

Altmühlsee covers 4.5 square kilometers of open water with multiple designated swimming zones and several small harbors scattered along the shoreline. Paved cycling routes circle the entire reservoir and connect neighboring villages on both sides.

Engineers created the reservoir in 1985 as part of a regional water management project to regulate river flows in central Franconia. Construction transformed a shallow valley into a controlled recreation area with managed water levels.

Local residents treat the reservoir as a weekend gathering spot for sailing clubs and family picnics. The name combines the old Altmühl river valley with the modern character of the created lake.

Large parking areas sit near the central access point, with shoreline reachable on foot within a few minutes. During warm months from April through October, visitors can rent watercraft and bicycles directly at the site.

The lake's dam, made of sand and clay, is 3 to 5.5 metres high and runs 12.5 kilometres around the entire shore, making it Germany's longest dam structure. Because of it, the water surface lies up to 3 metres above the surrounding land. Inside the dam, steel sheet piles driven down to the impermeable soil form a sealing wall.