The Werse [German pronunciation: [ˈvɛʁzə]] (river no. 32) is a 67-kilometre-long (42 mi), left-hand tributary of the River Ems in Münsterland, North Rhine-Westphalia in Germany. The catchment area of the Werse is 762.47 km². Its name may be derived from a pre-Indo-European language, Vasconic, from which the Basque language developed. Its water quality is Class II-III and, in places, Class II. Contamination from communal sewage farms, fish ponds, but especially diffuse contamination from agriculture pollutes the mass balance of the Werse and leads to eutrophication along the entire river course, especially in the retention basin areas.