Delta de la Sauer National Nature Reserve, National nature reserve in Bas-Rhin, France

The Delta de la Sauer National Nature Reserve covers 486 hectares at the confluence of the Sauer and the Rhine, between Seltz and Munchhausen in the Bas-Rhin. Its alluvial forests, wet meadows, reed beds and mudflats are crossed by a meander of the Rhine's former main course, which the Sauer now follows to reach the corrected riverbed. A blue rowboat with wooden oars lies on the cracked mud of the banks.

The landscape underwent major transformation in the 1840s when river management projects modified the Sauer's natural meanders and altered flooding patterns in the delta. These engineering changes reshaped the ecosystem and continue to influence conditions today.

The white willow stands in the delta are cut as pollards, a traditional practice that produces a low, dense canopy and lets visitors pass beneath by boat. The wood was harvested regularly, and the taller ground behind carries ash, oak and elm mixed with white poplar.

Walking paths with clear markings guide visitors through the different habitats, with observation points positioned for bird watching opportunities. Spring and autumn offer the best conditions when large migrating flocks pass through the area.

The reserve holds the near-only French population of the brown pelobate, a small nocturnal toad, and is one of the last French breeding sites of the field frog. Its 183 recorded bird species include 77 that nest here, and the delta is Alsace's largest black kite nesting area. In 2015 Grosswoerth hosted the Upper Rhine stork migration gathering.