The Lech (Licus, Licca) is a river in Austria and Germany. It is a tributary of the Danube and 248 km (117 miles) in length, with a drainage basin of 2,550 sq. miles.

Its source is located in the Austrian state of Vorarlberg, where the river rises from the Formarinsee (a lake) in the Alps at an altitude of 6,120 ft. It flows in a north-north-easterly direction and crosses the German border forming the Lechfall, a 12 m high waterfall; afterwards the river enters a narrow gorge (Lechschlucht). Leaving the Alps, it enters the plains at Fussen (2,580 ft.) in the German state of Bavaria where it formed the historic boundary with Swabia, runs through the city of Füssen and behind through the Forggensee (a lake). Here, it forms rapids and a fall.

The river flows further northwards through a region called the Lechrain and passes the cities of Schongau, Landsberg, Augsburg (where it receives the Wertach ) and Rain before entering the Danube River just below Donauworth (1,330 ft.). It is not navigable, owing to its torrential character and the gravel beds which choke its channel. There is a particularly magnifient view of the Lech valley from Neuschwanstein Castle, near Fussen.

On more than one occasion, historic events have been decided on the banks of this river. In April 1632, Gustavus II (Gustavus Adolphus) of Sweden defeated and mortally wounded Johan Tzerclaes, Count of Tilly. At Lechlfeld , a stony plain between the Lech and the Wertach, near Augsburg, Otto I defeated the Magyars in August 955.