Afon Clarach (Welsh pronunciation: [ˈklaraχ]; also known as the River Clarach) is a small river discharging into Cardigan Bay north of Aberystwyth.

It flows through a largely agricultural and forested landscape except in its lowest reaches where its banks are crowded with holiday developments.

The Clarach is formed at the confluence of the Afon Stewi and Nant Seilo at Penrhyncoch, with both their headwaters originating in low hills at the edge of the Plynlimon range.

[1] The course of the river takes it past the Institute of Biological, Environmental and Rural Sciences (a part of Aberystwyth University), and the village of Bow Street.

Consequently, Atlantic salmon and sea-trout are rare, however brown trout, brook lampreys, millers thumb and stone loach are commonly found.