The Aabach (also Aa, or Ustermer Aa for disambiguation with the Mönchaltorfer Aa) is a minor river in the canton of Zürich, Switzerland. At a length of , it flows from Pfäffikersee to the Greifensee. Its valley is known as Aatal ("Aa Valley"), eponymous of the settlement Aathal. Gallery References Rivers of Switzerland Rivers of the canton of Zürich 1Aabach Pfäffikersee