The River Dyfi (Afon Dyfi in Welsh) (also known in English as the River Dovey) is a river in mid Wales. It rises in the small lake Craiglyn Dyfi at about 1900 feet above sea level, below Aran Fawddwy, flowing south to Dinas Mawddwy and Cemmaes Road, then south west past Machynlleth to Cardigan Bay at Aberdyfi. It shares its watershed with the River Severn and the River Dee before flowing generally south-westwards down to a wide estuary. The only large town on its route is Machynlleth.
Because of its origins high in the Cambrian Mountains and its relatively short length, it is prone to flooding and some roads in the lower catchment can become impassable during very wet weather. It is a relatively pristine river with few polluting inputs and is notable for its Salmon and Brown Trout.
The catchment area was notable for its now defunct lead mines and slate quarries, especially around Corris and Dinas Mawddwy.