Türlersee, Natural lake in Affoltern district, Switzerland.

Türlersee is a lake on the border of Aeugst and Hausen am Albis at 643 m, about 1.4 km long and 500 m wide. A landslide from the Aeugsterberg around 10,000 years ago dammed the Reppisch, which leaves the lake at its northern end. The southeastern shore holds a campsite and the Türlen lido.

Around 10,000 years ago, at the end of the last ice age, a landslide on the Aeugsterberg sent 60 million cubic metres of molasse rock into the valley, damming the Reppisch and creating the lake. It first drained through the Hexengraben toward the Reuss, later through the Reppisch into the Limmat. A first protection ordinance was issued in 1944, revised in 1998 and 2001.

The lake's name comes from the hamlet of Türlen on its shore. A local legend tells that a farmstead once stood here; a girl cursed her treacherous father, lightning struck, and the ground opened into a lake. The 4 km Türlerseerundweg circles the water in about 65 minutes from the Hausen-Türlersee postbus stop.

The lake is best reached by car, with parking areas at several access points around the shore. Early arrival on summer weekends is advisable, as the lake becomes busy with swimmers and picnickers.

The lake was dammed about 10,000 years ago when 60 million cubic metres of rock slid from the Aeugsterberg, blocking the Reppisch. Originally it drained through the Hexengraben toward the Reuss; only later did it flow out via the Reppisch into the Limmat. A local legend instead tells of a farmstead that vanished into a fiery cleft, leaving a lake.