Aa is the name of a large number of small European rivers. Aa originated from an Indo-European word meaning water, and it can be seen in the German
ach or
aach or the
North Germanic a or
aa.
- Aa River (France), a river in northern France
- Aa River (Meuse), a river in North Brabant, Netherlands
- Aa of Weerijs, a river in North Brabant, Netherlands which joins the Mark at Breda
- Drentsche Aa, a river in Drenthe and Groningen, Netherlands
- Aabach (Greifensee), or Ustermer Aa, a river in Switzerland
- Aabach (Afte), formerly called the Große Aa, a river in Germany
- Aa (Möhne), a river in North Rhine-Westphalia, Germany
- Aa (Nethe), a river in North Rhine-Westphalia, Germany
- Aa (Werre), a river in North Rhine-Westphalia, Germany
- Aa, a river in Antwerp, Belgium which joins the Nete River
- Engelberger Aa, a river in Obwalden and Nidwalden, Switzerland
- Große Aa, a river in Lower Saxony, Germany
- Münstersche Aa, a river in Germany, one of several Westphalian rivers called Aa
- Sarner Aa, a river in Obwalden, Switzerland, tributary of Lake Lucerne
- Mussel Aa, a river in Groningen, Netherlands
- Pekel Aa, a river in Groningen, Netherlands
- Ruiten Aa, a river in Groningen, Netherlands
- Westerwoldsche Aa, a river in Groningen, Netherlands
- Aare, a river that runs through Bern, capital of Switzerland