Ems, river, 208 mi (335 km) long, rising in the Teutoburger Wald, NW Germany, and flowing NW into the North Sea near Emden. Its wide mouth is called the Dollart. The Ems is paralleled for much of its course by the Dortmund-Ems Canal. The Emsland is a swampy region between the lower course of the Ems and the Dutch border. Extensive drainage projects (begun 1928) have reduced the moors and swamps. Oil and natural-gas fields were developed in the region after 1940.