A shallow artificial lake on the Reuss four kilometres south of Bremgarten, created by a low weir at Rottenschwil. The shallow water attracts migrating waders and waterfowl — the area is now a federal-level wetland reserve and one of the best birdwatching spots in the Aargau, with hides set up along the eastern bank.
A flat cycle path follows the river from Bremgarten down to the Flachsee and on to Rottenschwil, making for a pleasant afternoon ride. In summer the bank at Hermetschwil-Staffeln has a free swimming spot, popular with locals.