Altabgrabung Klingenberger, Nature reserve in Langenfeld, Germany.

Altabgrabung Klingenberger is a protected nature reserve in Langenfeld that centers on a lake with several constructed islands scattered across its surface. Dense thickets of alder and willow shrubs coat the surrounding slopes, covering much of the 26-hectare site.

Gravel was extracted from this site on the southwestern edge of Langenfeld before it was fenced off and left to regenerate. In 1984 the roughly 26-hectare former pit was designated a nature reserve under the code ME-019. In the 1990s numerous islands topped with coarse gravel were piled up in the lake, and most have since been overgrown by willows, alders and brambles.

The reserve serves as a refuge where rare bird species and other wildlife follow their natural patterns largely undisturbed. The thick growth of alder and willow trees creates an environment shaped entirely by ecological processes rather than human intervention.

The reserve is completely fenced and there is a ban on entering and fishing, so it cannot be visited from inside; the lake is screened by alder and willow thickets and is not visible from outside. The L 43 (Hitdorfer Straße) borders the site to the southeast, the A 59 to the west and a railway line to the north, so views are only possible from these edges.

The lake regularly hosts the large pond mussel, a species listed as strongly endangered in Germany. In the 1990s the bitterling, a rare fish in North Rhine-Westphalia, was introduced and established itself here; it lays its eggs inside these mussels.