The Sieg is a 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 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...

 and Rhineland-Palatinate

Rhineland-Palatinate

Rhineland-Palatinate is one of the 16 states of the Federal Republic of Germany. It has an area of and about four million inhabitants. The capital is Mainz. English speakers also commonly refer to the state by its German name, Rheinland-Pfalz ....

, 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...

 named after the Sigambrer. It is a right tributary of the Rhine and 153 kilometres in length.

The source is located in the Rothaargebirge

Rothaargebirge

The Rothaargebirge is a low mountain range reaching heights of up to 843.1 m in North Rhine-Westphalia and Hesse, Germany....

 mountains. From here the river runs southwestwards to the city of Siegen

Siegen

Siegen is a city in Germany, in the south Westphalian part of North Rhine-Westphalia.It is located in the district of Siegen-Wittgenstein in the Arnsberg region...

 and the hills of Siegerland

Siegerland

The Siegerland is a region of Germany covering the old district of Siegen and the upper part of the district of Altenkirchen, belonging to the Rhineland-Palatinate adjoining it to the west.Geologically, the Siegerland belongs to the Rheinisches Schiefergebirge...

, both named after the river. Further west the Sieg valley forms the boundary of the Bergisches Land

Bergisches Land

The Bergisches Land is a low mountain range region within the state of Nordrhein-Westfalen, Germany, east of Rhine river, south of the Ruhr. The landscape is shaped by woods, meadows, rivers and creeks and contains over 20 artificial lakes...

 (northern) and Westerwald

Westerwald

The Westerwald is a low mountain range on the right bank of the River Rhine in the German federal states of Rhineland-Palatinate, Hesse and North Rhine-Westphalia. It is a part of the Rhine Massif...

 (southern). The river finally runs through a protected area east of the city of Bonn

Bonn

Bonn is the 19th largest city in Germany. Located in the Cologne/Bonn Region, about 25 kilometres south of Cologne on the river Rhine in the State of North Rhine-Westphalia, it was the capital of West Germany from 1949 to 1990 and the official seat of government of united Germany from 1990 to 1999....

.

After passing the cities of Hennef

Hennef

Hennef is a town in the Rhein-Sieg district of North Rhine-Westphalia, Germany. It is situated on the river Sieg, approx. 7 km south-east of Siegburg and 15 km east of Bonn. Hennef is the fourth biggest town in the Rhein-Sieg-Kreis Hennef (Sieg) is a town in the Rhein-Sieg district of...

 and Siegburg

Siegburg

--122.148.78.228 05:06, 14 November 2011 Siegburg is a city in the district of Rhein-Sieg-Kreis, in North Rhine-Westphalia, Germany...

it joins the Rhine near Niederkassel/Mondorf just a few kilometres north of the centre of Bonn.