Reißinsel, Nature reserve on Rhine River island in Mannheim, Germany.

Reißinsel is a 100-hectare nature reserve in a Rhine bend west of Mannheim-Neckarau, not a true island. It is bounded by the Rhine and the narrow Bellenkrappen arm, and together with the Waldpark forms 275 hectares without dikes, regularly flooded. The northern part is Bannwald left untouched; the rest is Schonwald. Softwood floodplain with silver willows and poplars gives way to hardwood with pedunculate oaks, ashes and hornbeams, plus flood channels and a large meadow orchard.

Carl Reiß bought the peninsula in 1881 to extract clay from its soil. After mining ended, he handed the land over to Mannheim as a recreational space, and it was eventually placed under nature protection.

The name Reißinsel comes from Carl Reiß, the industrialist who donated the land to the city. Walkers today can observe how the Rhine continues to shape the terrain through seasonal flooding, leaving behind patterns in the soil and vegetation.

A loop trail runs through the forest and is open for walking, but access is restricted from March to June during the bird breeding season. The ground can be muddy after rain, so sturdy footwear is a good idea.

The northern section is managed as Bannwald, a legal status that halts all forestry work and leaves the woodland to develop on its own. The rest of the Reißinsel is Schonwald, a less strict category. The Bannwald and Schonwald zones were established in 1982 after four of the five public entrances were closed.