The Avren's waters were gray and white. Its banks sloped down from green uplands on both northern and southern sides. Many rivers flowed down into the Avren, such as the River Tevvyn in the west; the River Ystrad in the middle of the land; and in the east the so-called Small Avren. File:Prydain Map.jpg The Great Avren was the river in which, during the events of The Book of Three, Taran almost drowned, professing to Gwydion that he had been sure he could swim once he came to do it.