Aa (Werre)

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Aa
North Rhine-Westphalia
Location
Country	Germany
State	North Rhine-Westphalia
Physical characteristics
Mouth
• location	Werre
• coordinates	52°07′25″N 8°40′13″E / 52.1236°N 8.6703°E / 52.1236; 8.6703
Length	26.0 km (16.2 mi) [1]
Basin size	256 km2 (99 sq mi) [1]
Basin features
Progression	Werre→ Weser→ North Sea

Aa (also: Westfälische Aa, "Westphalian Aa") is a river of North Rhine-Westphalia, Germany. It is a left tributary of the Werre, which it joins in Herford. It is formed by the confluence of two small streams in Bielefeld-Milse. In its upper part, it is called Johannisbach.