Sylvensteinsee, Reservoir in Lenggries, Germany.

Sylvensteinsee is a reservoir in Lenggries, Germany, stretching between mountains in Upper Bavaria. Unpaved trails wind along the shoreline and pass through pine woods to reach quiet coves with gravel beaches.

The dam was built between 1954 and 1959 to keep the Isar's water level steady, after the Walchensee and Achensee power plants had diverted much of the river's flow; flood protection was a secondary aim. The village of Fall was demolished before the flooding and rebuilt a few dozen metres higher on the road to Vorderriß. The dam was raised by 3 m between 1994 and 2001, and on 23 August 2005 the reservoir reached its maximum and the gate had to be opened.

The lake takes its name from the Sylvenstein, a rock ridge that narrows the upper Isar valley to the east; the western boundary is the rocky Hennenköpfl. The former village of Fall was demolished before the flooding and rebuilt a few dozen metres higher on the road toward Vorderriß. The lake is a popular excursion and recreation area.

A regional train to Lenggries station followed by a mountain bus brings visitors to the lake. Those who hike or cycle should plan several hours to explore the trails along the shore.

The village of Fall was demolished before the water rose and rebuilt a few dozen metres higher along the road toward Vorderriß. The lake was originally planned much larger, reaching as far as Vorderriß. During the June 2013 flood the water stood 13 m above its usual level.