Klingnauer Stausee, Reservoir and Ramsar site in Aargau, Switzerland

Klingnauer Stausee is a reservoir in the canton of Aargau, Switzerland, formed by a dam on the Aare River. It covers open water, reed beds, wet meadows, and stretches of willow and ash woodland along its banks.

A dam was built on the Aare River in the 1930s to generate hydroelectric power, and the water held back formed the reservoir seen today. In 1990, the site received international protection as a Ramsar wetland.

The name Klingnauer Stausee comes from the nearby town of Klingnau. The site draws birdwatchers who walk the shoreline paths with binoculars, looking for wading birds and waterfowl across the open water and reed beds.

The reservoir lies between Klingnau on the right bank and Böttstein and Leuggern on the left, about a kilometre before the Aare joins the Rhine. The 2003 Klingnauer Beobachtungsturm observation tower stands on the shore at Kleindöttingen. The Surb enters the Aare at the head of the reservoir.

The reservoir's water level is not left to the river: the weir between the flood embankments controls it, and the drawdown exposes mudflats that migratory waders use. The lake is about three kilometres long and up to 500 metres wide, and most of its surface lies in the municipality of Leuggern, not Klingnau.