Rettbergsaue Nature Reserve: A Protected Floodplain Island in the Upper Rhine Valley of Hesse

Rettbergsaue is a river-built island formed after the last cold period, when the Rhine deposited layers of sand and clay in this stretch of the Upper Rhine valley. For centuries the island existed as two separate landforms, the Biebricher Wörth and the Schiersteiner Wörth. The western section, which was called Karthäuser-Aue in the late Middle Ages, was purchased in 1832 by Carl von Rettberg, a Nassau officer and adjutant to the duke, from whom the island takes its present name. Rettberg attempted livestock and horse breeding there, but financial difficulties forced him to return the property to the Duchy of Nassau only a few years later.

In the early twentieth century, the island developed into a recreational venue. In 1914 the Schiersteiner Strandbad opened at the western end near two former side arms of the Rhine, and in 1921 the Biebricher Strandbad was added along the northern bank. Both bathing facilities were closed in 1962 because the Rhine had become heavily polluted, but the open spaces were redesigned as day-use leisure grounds. A pivotal moment came in the early 1970s, when plans called for a major recreation and tourism development on the island, including holiday apartments, a riding stable, sports facilities, seminar buildings, walking trails, and even a cable car link to Biebrich, as well as a power plant. The 1978 designation of the island as a nature reserve effectively ended those plans and shifted its trajectory toward conservation.

Subsequent decades saw further protection measures. The original nature reserve was enlarged in 1984, and in 2001 an FFH (Habitats Directive) site was added around the island as part of the European Natura 2000 network. In 2009 the local branch of the German Federal Agency for Technical Relief (THW) dredged a channel in the side arm to remove accumulated silt and odors and help restore the bathing landscape. Between 2013 and 2025, public access via the historic stairway from the Schiersteiner Bridge was interrupted by the construction of a new bridge; a barrier-free access route was reopened in 2025.

Ecologically, Rettbergsaue belongs to the category of Upper Rhine floodplain habitats that have become rare in central Europe. The island preserves both a functioning softwood pioneer zone and a much rarer remnant of hardwood floodplain forest, an assemblage once widespread along the Rhine and now confined to a handful of protected sites. The woodland is dominated by ash, elm, sycamore, Norway maple, and pedunculate oak, with a structurally rich understory shaped by seasonal flooding.

Around and between the wooded areas, the island sustains a mosaic of open habitats. Auewiesen, or floodplain meadows, occupy flatter sections; shrub and herbaceous edges line the woodland margins; pioneer and flood meadows colonize freshly exposed sediments; nitrophilous tall-herb communities thrive on nutrient-rich deposits; and the shoreline includes both soft pioneer vegetation and dynamic sand and mud communities that change with each flood event. Together, these habitats support a broad range of invertebrates, plants, and mammals typical of large European lowland rivers, and form a continuous gradient from aquatic to fully terrestrial environments.

The protected designation of the area reflects this habitat diversity. The nature reserve Rettbergsaue bei Wiesbaden was established to safeguard the island as a breeding and resting site for threatened bird species and as a refuge for the endangered hardwood floodplain community, while the surrounding FFH area was drawn more broadly to encompass the full range of riverine, woodland, meadow, and shoreline habitats associated with the site.

Birds are the most prominent and best-documented wildlife group on Rettbergsaue. In the late 1990s, surveys recorded nineteen occupied Black Kite nests on the island, marking it as an unusually important breeding ground for this species in the region. The wider bird community spans raptors, woodland birds, and open-country species, and includes Red Kite, European Honey Buzzard, Common Kingfisher, Red-backed Shrike, Wood Lark, Common Nightingale, Bluethroat, Common Redstart, and Grey-headed, Middle, and Lesser Spotted Woodpeckers.

Beyond birds, the island supports typical Rhine floodplain mammals such as wild boar, whose activity is visible in tracks and rooting signs along the woodland edges, and Grey Herons, which feed along the shallows and roost in the taller trees. The combination of closed canopy, open meadows, dynamic shorelines, and shallow side arms creates a varied vertical and horizontal structure that sustains a wide food web, from aquatic invertebrates in the side channel to raptors hunting over the meadows and woodland birds nesting in mature trees.

The role of the island as a refuge for these species is recognized at both national and European levels. Its inclusion in the EU bird protection area Inselrhein, which extends from Mainz downstream toward Lorch, places Rettbergsaue within one of the most important continuous bird corridors along the middle and upper Rhine.

Conservation is the central organizing principle of how Rettbergsaue is managed today. In 1978 the island was designated as the nature reserve Rettbergsaue bei Wiesbaden, covering 52.6 hectares and making it the oldest formally protected site within the current list of nature reserves of the city of Wiesbaden. The reserve's purpose was explicit: to protect the island as a breeding and resting habitat for threatened bird species and to safeguard the surviving patch of hardwood floodplain forest, a vegetation type that had become exceptionally rare along the Rhine.

In 1984 the reserve's area was expanded to 67.78 hectares, extending protection closer to the full footprint of the island. A second layer of protection came in July 2001, when an FFH (Habitats Directive) site of about 71 hectares was designated around the island and integrated into the Natura 2000 network. This designation acknowledges the full habitat mosaic, including softwood and hardwood floodplain forest, shrub edges, floodplain meadows, herbaceous fringes, shoreline and drift-line biotopes, pioneer and floodplain grasslands, nitrophilous tall-herb communities, and newly formed sediment habitats.

Rettbergsaue is also embedded in larger conservation networks that extend well beyond the island itself. It forms part of the FFH area Wanderfischgebiete im Rhein, a 1,269-hectare site covering migratory fish habitats along the river from the Kühkopf through the Inselrhein to Bacharach in the Middle Rhine valley. It is likewise included in the EU bird protection area Inselrhein, which runs from Mainz downstream toward Lorch. Together, these designations make the island a small but high-value component of one of the more strictly protected stretches of the German Rhine.

Rettbergsaue's cultural significance is closely tied to the city of Wiesbaden and especially to its riverside districts of Biebrich and Schierstein. The island sits directly opposite Biebrich Palace, one of the most prominent historical residences in the region, and historically formed part of the visual foreground of this Baroque and Classical palace setting. The combination of palace, river, and wooded island has long shaped the image of this stretch of the Rhine.

In the early twentieth century the island became an everyday recreational landmark for local residents. The opening of the Schiersteiner Strandbad in 1914 and the Biebrich Strandbad in 1921 turned the island into a popular bathing destination at a time when many urban dwellers did not travel far for leisure. Even after these facilities were closed in 1962, the island retained its role as a nearby outdoor space, with sand areas, playgrounds, sports fields, and grill areas that continue to be used by families from Wiesbaden.

The name itself reflects this layered history. The western part of the island, formerly known as Karthäuser-Aue after Carthusian religious influence in the late Middle Ages, took its current name Rettbergsaue from Carl von Rettberg, a Nassau officer who acquired it in 1832. The seasonal passenger ferry Tamara, connecting Schierstein, the island, and Biebrich, is a continuing element of this regional leisure culture and remains a recognizable local tradition each summer.

Rettbergsaue stands out for the unusual combination of features it packs into a small area: a sizeable natural Rhine island, a remnant hardwood floodplain forest, a robust population of breeding raptors and songbirds, and a formal cascade of conservation designations culminating in Natura 2000 status. Its accessibility from Wiesbaden, Biebrich, and Schierstein makes it a working example of how riverine nature protection and everyday public recreation can coexist along the Rhine.

The island's ecological profile is shaped by its position between the main Rhine channel and the calmer Wachsbleicharm. This dual exposure produces a gradient from dynamic, disturbed shoreline habitats to stable alluvial woodland, supporting very different species communities within a short distance. The historical role of the island, from late medieval Carthusian associations through nineteenth-century private ownership to early twentieth-century bathing culture, adds a human dimension that complements its ecological importance.

The character of Rettbergsaue shifts meaningfully with the seasons, although many of its core qualities, in particular woodland structure, can be appreciated year-round. Spring and early summer are the strongest periods for birdwatching, when breeding activity intensifies and species such as Black Kite, Red Kite, and various woodland songbirds are most visible across the meadows and forest edges. Floodplain vegetation, including herbaceous fringes and meadow plants, also peaks in late spring and early summer.

Summer brings the liveliest public experience of the island. Family-oriented leisure areas are in full use, the playground and beach-like spaces attract local visitors, and the seasonal passenger ferry Tamara operates between Biebrich, Schierstein, and the island. Late summer and early autumn tend to be quieter and more conducive to focused nature observation. Winter visits offer a different appeal: bare trees make the forest structure and birdlife easier to observe, and the river landscape takes on a more austere, sculptural quality, though visitors should be aware that high water events and bridge construction phases have historically influenced access.