Aa is a river of 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...

, 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...

. It is 7.4 km long and is a left tributary of the Möhne

Möhne

The Möhne is a small-size river in western Germany , right tributary of the Ruhr. The Möhne passes the towns of Brilon, Rüthen, Warstein. There is large articifical lake near the mouth of the river, the Möhne Reservoir, used for hydro power generation and leisure activities....

 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...

. The river has a watershed of 23.071 square kilometres.

The source of Aa in the village of Altenbüren. From here it flows in an easterly direction. At 473 metres its course meanders to the north. Nearby the Hillbringse

Hillbringse

Hillbringse is a river of North Rhine-Westphalia, Germany....

 flows in from the south. Half a kilometer farther are five former mills in Aatal, called Aamühlen. The Fülsenbecke

Fülsenbecke

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

flows in near here from the north. The Aa overcomes a height difference of 72 meters, which corresponds to an average bed slope of 9.7 %.