The Geul (-Dutch, in Göhl, in Gueule) is a river in Belgium and the Netherlands. It is a right tributary to the river Meuse. The source of the Geul is near the German-Belgian border south of Aachen at approx. 300 m altitude. After approx. 20 km it flows into the Netherlands, and after 58 km it flows into the river Meuse, north of the city Maastricht. A tributary of the river Geul is the Gulp. Towns along the Geul are Kelmis (Belgium), Valkenburg aan de Geul and Meerssen (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 (La Calamine) and Plombières (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 limestone) 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).