The Mūša (Latvian: Mūsa; German: Muhsse) is a river in Northern Lithuania and Southern Latvia (Zemgale region). At its confluence with the river Nemunėlis (Latvian: Mēmele) in Latvia, near the city of Bauska, the river Lielupė is formed. The river is 164 kilometers (146 km in Lithuania, 18 km in Latvia) long.