Flachsee

Flachsee is a man-made lake on the Reuss river at Rottenschwil in the Swiss canton of Aargau, a few kilometres south of Bremgarten. It filled in 1975 in the backwater of the Bremgarten-Zufikon hydropower plant, as part of the wider Reusstal landscape restoration. Today it is a nationally important reserve for waterbirds and migrating birds, and one of the better birdwatching spots in the region.

What is Flachsee and why visit?

Shallow water, muddy margins and slow-moving stretches create a habitat that is rare in the surrounding, heavily engineered river plain. Since 1973 observers have recorded 212 bird species here. The area is listed in the federal inventory of water and migratory bird reserves (object no. 106) and protected under the WZVV ordinance. The Stiftung Reusstal foundation, based in the Zieglerhaus in Rottenschwil, is among those looking after the Reusstal.

Which birds can you see?

• Breeding season: the lake is an important nesting site for the northern lapwing, alongside several other water and wetland birds.
• Spring and autumn: waders such as common snipe and green sandpiper stop over on exposed mud in the slower-flowing sections.
• All year: a mix of ducks and other waterfowl, with the highest species counts outside the breeding season.

Observation facilities are placed along the paths, including a viewing mound and a covered hide on the recommended walking loop. The hide lets you watch birds without disturbing them, so bring binoculars or a telephoto lens.

How do you get to Flachsee?

The easiest public transport option is the PostBus to the Hecht stop in Rottenschwil. By car, park near the Reuss bridge in Rottenschwil, where the walk along the shore begins. The lake lies at roughly 47.328 N, 8.369 E.

When should you go, and how should you behave?

Variety peaks during spring and autumn migration, and lapwings breed in spring. Pack binoculars and warm layers, since the shore can be windy. This is a protected reserve, so stay on the marked paths, keep noise down and follow the on-site signs. Check stiftung-reusstal.ch before your visit for current rules, for example on dogs.

Frequently asked questions

Is Flachsee a natural lake? No. It was created in 1975 after the Bremgarten-Zufikon dam was built on the Reuss.

How many bird species have been recorded? According to the canton of Aargau, 212 species since 1973.

Where is the best place to watch birds? From the covered hide on the walking loop and from the viewing mound.

How do I get there without a car? Take the PostBus to the Hecht stop in Rottenschwil, then walk a short way to the shore.