Gusen, River, Upper Austria, northern tributary of the River Danube east of Linz, in the central Muehlviertel region. The river originates from the confluence of the Kleine Gusen and the Grosse Gusen rivers, which both rise south of Schenkenfelden (alt. 738 m) and merge south of Gallneukirchen (alt. 337 m) to form the River Gusen. South of St. Georgen an der Gusen, the River Gusen flows into the River Danube; castles and castle ruins. The route of the former horse-drawn railway Linz- Budweis (Budvar, Czech Republic) ran along the Kleine Gusen river. At St. Georgen the medium flow rate of the River Gusen is 2.2 m3/sec.