The Prien is a river of Bavaria, Germany.

Its source is at 1,150 metres (3,770 ft) above sea level at the Spitzstein. After 33 kilometres (21 mi) it discharges into the Chiemsee at the bay Schafwaschener Bucht. It is one of the longest mountain streams in the Bavarian Alps. The name probably derives from the Celtic name of the river, Brigenna, the one coming from the mountains (female) in Celtic languages. The town Prien am Chiemsee was named after the river. Before Prien, on a weir the Mühlbach [de] is fed, which flows independently into the Chiemsee further southward.

The Prien is, after the Tiroler Achen, the second largest tributary to the Chiemsee.

• List of rivers of Bavaria