Blau (Danube)

The Blau (German pronunciation: [blaʊ] ^ⓘ) is a 22-kilometre-long (14 mi) river in Baden-Württemberg, southern Germany, and a left tributary of the Danube. The source of the Blau is the karst spring of Blautopf, in the town Blaubeuren, in the Swabian Jura. It flows east through Blaustein to the city of Ulm, where it empties into the Danube.

Blau
The Blau in Ulm's historic "Fischerviertel", about 300 m before it flows into the Danube
Location
Country	Germany
State	Baden-Württemberg
Physical characteristics
Mouth
• location	Danube
• coordinates	48.38°N 9.7861°E / 48.38; 9.7861
Length	22.2 km (13.8 mi)[1]
Basin size	499 km2 (193 sq mi)[1]
Basin features
Progression	Danube→ Black Sea

The course of the Blau from Blaubeuren to Ulm (Postcard by Eugen Felle, ca. 1900)

Blau valley

The valley of the Blau was formed by the Danube. When the Swabian Jura rose, the Danube initially incised a deeper and deeper valley but finally chose a course to the southwest. In the valley it left behind today, the Schmiech river flows south meeting the Danube in Ehingen (Donau), whereas the Blau flows east towards Ulm.