The Große Aue rises at a height of as the Aue on the southern side of the Wiehen Hills in the village of Dono in the parish of Rödinghausen in North Rhine-Westphalia. After one and a half kilometres it turns north and from its confluence with the Nordbach, which joins it from the west at Schwenningdorf, is known as the Große Aue. It crosses a water gap in the Wiehen Hills, losing 40 metres of height and powering two mills, so that in the section through the Wiehen crest it has been named the Neuer Mühlbach after the Neue Mühle at Schwenningdorf. Further downstream near Fiegenburg it collects a tributary from the west which drains the entire , and is then known as the Mühlbach, powering the mill at Gut Grollage, east of the Egge in front of the main crest of the Wiehen Hills. At Bad Holzhausen it loses the name Mühlenbach. Here the Große Aue reaches the North German Plain. At 10.6 kilometres it passes under the Mittelland Canal. On the western edge of Espelkamp in the river meadows on the far side of the dyke, two small lakes have been laid out: the Großer Auesee and the See am Kleihügel. The river continues north, passing Rahden to the west, to Preußisch Ströhen, here it picks up the waters of the Großer Dieckfluss,before crossing the border into Lower Saxony. Here the valley is part of the 'bog belt'. Between kilometres 62.8 and 58.8 the Großer Aue flows in two parallel channels, of which one has been straightened, the other is the first part of a renaturalised route. Through Wagenfeld-Ströhen the Großer Aue runs to Barenburg. It flows eastwards through the southern part of the Sulingen Gap and is then forced south by the geest hills of the Steyerberg Forest. Beyond Steyerberg it turns towards the northeast and reaches after a few kilometres the Weser Depression, on whose western edge it flows through Liebenau, in order five kilometres later near Binnen, half way to Nienburg, discharging into the River Weser. Its total length is about.
Renaturalisation
After everything had been done in the years after the Second World War to turn the Große Aue into a canal-like river and thereby to create a flood-free river channel, initiatives during the 1980s in the Minden-Lübbecke region led to the decision to renaturalise the landscape. The intent was to enable the area, which had lost many of its native plant and animal species, to recover. A habitat was to be created to support riparian woods, hedges and plants and animals typical of the area.
When the first cut of the spade for the renaturalisation took place in 1989 this project was unique in North Rhine-Westphalia. The monotonous river bed and riverside strips of land up to 300 m wide were turned into near-natural pastureland again. About of flood plain was created. The artificial water channel was largely retained, but parallel to it a new river course was laid out which ran along the old route in several places. Today it is clear that a rich animal and plant world has been created without the risk of major flooding.
Fauna and flora
A valuable habitat has been generated on the Große Aue for plants and animals typical of water meadows. In the wet biotopes and in the standing and flowing waters there are grass rushes, water violets and blister sedges as well as short-winged coneheads and large marsh grasshoppers. Threatened dragonflies, such as the banded darter, southern emerald damselfly live here as do birds like the whitethroat and little grebe. Reed buntings, reed warblers and snipe also occur here. The near-natural grassland and wet meadows in the upper reaches of the river near Rödinghausen are under nature conservation protection. The nature reserve has an area of and is known as the Aubach Valley Nature Reserve. Particularly valuable are the rich wet meadows and pastures with their sedges and reed beds.
Tributaries
Its tributaries include the Flöthe and the Kleine Aue, that join it from the east, and the Großer Dieckfluss, which flows westwards, and merges into the Großer Aue at Preußisch Ströhen, at L = left-hand, R = right-hand tributaries looking downstream
