The Ay (, Äy; ) is a river in Bashkortostan and Chelyabinsk Oblast in Russia, a left tributary of the Ufa. The river is 549 km long, and its drainage basin covers 15000 km2. The Ay freezes up in late October or early November and remains icebound until mid-April. The cities of Zlatoust and Kusa are along the river Ay. There are many steep cliff sides and caves along the banks of the river. The current of the Ay has been used for generating hydroelectric power. It is also possible to fish for pike, bleak, and carp, to name a few species.