The Geul is a river in Belgium

Belgium

Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 and the Netherlands

Netherlands

The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

. It is a right tributary to the river Meuse

Meuse River

The Maas or Meuse is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea...

. The source of the Geul is near the German-Belgian border south of Aachen

Aachen

Aachen has historically been a spa town in North Rhine-Westphalia, Germany. Aachen was a favoured residence of Charlemagne, and the place of coronation of the Kings of Germany. Geographically, Aachen is the westernmost town of Germany, located along its borders with Belgium and the Netherlands, ...

 at approx. 300 m (984 ft) altitude. After approx. 20 km (12 mi) it flows into the Netherlands, and after a further 38 km (24 mi) it flows into the river Meuse

Meuse River

The Maas or Meuse is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea...

, north of the city Maastricht

Maastricht

Maastricht is situated on both sides of the Meuse river in the south-eastern part of the Netherlands, on the Belgian border and near the German border...

. A tributary of the river Geul is the Gulp River

Gulp River

Gulp River is a river of Belgium. It flows for 22 kilometres through the province of Liège in the northern-central part of the country....

. Towns along the Geul are Kelmis

Kelmis

Kelmis is a municipality located in the Belgian province of Liège. On January 1, 2006, Kelmis had a total population of 10,396...

 (Belgium), Valkenburg aan de Geul

Valkenburg aan de Geul

Valkenburg aan de Geul is a municipality in the southeastern Netherlands.-History:Siege and conquest were characteristic of the history of Valkenburg. Each event is withheld, followed by subsequent restorations. This most definitely holds for the castle perched atop of a hill in the middle of the...

 and Meerssen

Meerssen

Meerssen is a place and a municipality in southeastern Netherlands.-History:The Treaty of Meerssen was signed in Meerssen in 870. The Treaty of Meerssen was an agreement of the division of the Carolingian Empire by the surviving sons of Louis I, Charles II of the West Franks and Louis the German...

 (Netherlands).

The river Geul is one of the most important sources of heavy metal inflow into the river Meuse. This is caused by the former zinc and lead mining activities near the Belgian towns of Kelmis

Kelmis

Kelmis is a municipality located in the Belgian province of Liège. On January 1, 2006, Kelmis had a total population of 10,396...

 (La Calamine) and Plombières

Plombières

Plombières is a Walloon municipality located in the Belgian province of Liège. On January 1, 2006, Plombières had a total population of 9,672. The total area is 53.17 km² which gives a population density of 182 inhabitants per km². The municipality Plombières consists of the villages...

 (formerly named Bleiberg). The last mines have closed early in the 20th century. One of the reasons for giving up mining activities in Plombières was the occasional flooding of the mine by the river Geul, as the bedrock (mainly Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

) contains many faults and fissures. Although the mine factory buildings have been demolished, old railway dikes are still abundantly present in the area. These provide ideal hiking routes, famous for the presence of the so-called "zinc flora" (including zinc-tolerant plants such as the yellow calamine violet, Viola calaminaria).