The Aabach, formerly called the Große Aa, is a 14 km long river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in Germany

Germany

Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, a left tributary of the river Afte

Afte

Afte is a river of North Rhine-Westphalia, Germany.-See also:*List of rivers of North Rhine-Westphalia...

. It rises in eastern North Rhine-Westphalia

North Rhine-Westphalia

North Rhine-Westphalia is the most populous state of Germany, with four of the country's ten largest cities. The state was formed in 1946 as a merger of the northern Rhineland and Westphalia, both formerly part of Prussia. Its capital is Düsseldorf. The state is currently run by a coalition of the...

 near the border with Hesse

Hesse

Hesse or Hessia is both a cultural region of Germany and the name of an individual German state.* The cultural region of Hesse includes both the State of Hesse and the area known as Rhenish Hesse in the neighbouring Rhineland-Palatinate state...

, between Bad Wünnenberg

Bad Wünnenberg

Bad Wünnenberg is a town in the district of Paderborn, in North Rhine-Westphalia, Germany. It is situated on the river Aabach, approx. 20 km south of Paderborn....

 and Marsberg

Marsberg

Marsberg is a town in the Hochsauerland district, in North Rhine-Westphalia, Germany.-History:Although its origins are obscure, Marsberg was a prospering town by the 13th century . It was a free city until 1807, when it was incorporated into the Kingdom of Westphalia, until 1813...

. Its source is where the regions Briloner Höhen and Sindfeld meet, in Brilon

Brilon

Brilon is a town in North Rhine-Westphalia, Germany, that belongs to the Hochsauerlandkreis.- Geography :Brilon is situated on the Brilon Heights at an altitude of about 450 m on the upper reaches of the river Möhne...

-Madfeld. From there it flows north between up to 503 m high mountains through a wonderful forested landscape, partly in the natural park Diemelsee

Diemelsee

Diemelsee is a community in Waldeck-Frankenberg in northwest Hesse, Germany, and is part of the Upland region.-Location:Diemelsee lies in the River Diemel in the Diemelsee Nature Park just upstream from and southwest of the Diemelsee reservoir...

. After a few kilometers it flows into the artificial lake Aabachstausee. It flows to the north and empties only about 3.5 km further north after Bad Wünnenberg, where it flows into the Afte. The drainage area of the Aabach reaches the divide

Water divide

A drainage divide, water divide, divide or watershed is the line separating neighbouring drainage basins...

 between the Weser and Rhine river basins: the Aabach flows to the north and drains into the Rhine via the Afte, Alme

Alme River

The Alme is a 50 km long river in North Rhine-Westphalia, Germany. It is a left tributary of the Lippe, into which it flows near Paderborn. The Alme defines the Alme Valley and flows through the towns Büren, Borchen and Paderborn.- Tributaries :...

 and Lippe River

Lippe River

The Lippe is a river in North Rhine-Westphalia, Germany. It is a right tributary of the Rhine and in length.The source is located at the edge of the Teutoburg Forest in Bad Lippspringe close to the city of Paderborn. It runs westward through Paderborn, Lippstadt and then along the northern edge...

s, while the small rivers that rise on the southern side of the ridge drain into the Weser through the Hoppecke

Hoppecke

Hoppecke is a river of Hesse, Germany....

 and Diemel

Diemel

The Diemel is a river in Hesse and North Rhine-Westphalia, Germany, left tributary of the Weser. Its source is near Willingen, in Sauerland. The Diemel flows generally northeast through the towns Marsberg, Warburg and Trendelburg. It flows into the Weser in Bad Karlshafen. The total length of the...

.