Siegaue, Nature reserve in Niederkassel, Germany.

Siegaue is a protected area along the Sieg River in Niederkassel, covering floodplain meadows, riverside woodland, and shallow river channels. The terrain is flat and open, with the river winding through it in broad curves.

The Siegaue nature reserve was designated in 1985, covering 535 hectares. It borders the smaller Siegmündung reserve, established in 1983 on Bonn city territory with 150.87 hectares. The boundary between the two reserves follows the Sieg River from southwest of Meindorf to its mouth. The Siegmündung reserve traces its origins to the Fischerei-Bruderschaft zu Bergheim an der Sieg, a fishing brotherhood practicing sustainable fishing since 987 with its own boundary stones.

The name Siegaue simply means the floodplain of the Sieg River, which describes exactly what you see: flat meadows that the river regularly covers with water. Along the paths, visitors can notice that some bordering fields are still used as grassland by local farmers, much as they have been for generations.

The reserve is accessible from several small parking areas on its edges, with marked walking paths that lead through the different parts of the area. Dogs must be kept on a leash, and visitors are asked to stay on the marked paths.

The Siegmündung is considered geomorphologically the best-formed river mouth of the Middle Rhine valley, with near-natural flooding dynamics. The adjacent Siegaue was designated in 1985, while the smaller Siegmündung reserve on Bonn's territory dates from 1983. Large parts have been registered as a Natura 2000 area since 2004.