St. Tydecho seems to have been quite a local benefactor, and one legend tells of how during a famine he changed the upper reaches of the Dyfi, just below Craiglyn Dyfi, into milk - and this stretch of the river is still called Llaethnant (Milk Brook) to this day.
George Borrow, in his book "Wild Wales", published in 1862, describes meeting a man way up above Llanymawddwy. They discuss the source of the river, and whether there are any Efync (plural of Afanc - see my notes on Llyn Barfog) there. The man says that they have all been killed long ago by Hu Gadarn and his humpty oxen. They go on to talk about a waterfall called "Fountain of the Royal Dyfi", and a nearby hill called Tap Nyth yr Eryri, which refers to eagles' nests, although eagles no longer nested there.