There's a passing mention in Brut y Tywysogion (Chronicle of the Princes) in 1109 AD of a ship from Ireland lying in Aber Dyfi, where Aber Dyfi in this instance is taken to mean the river, not the village, which wasn't established until many hundreds of years later.
In the 1200s, Geraldus Cambrensis mentions the river at least twice. In his book "The Description of Wales" he writes "From the snowy mountains of Eryri flows the noble river Devi, dividing for a great distance North and South Wales".
In "The Itinerary of Archbishop Baldwin Through Wales" he states "Approaching to the river Devi, which divides North and South Wales, the bishop of St. David's, and Rhys the son of Gruffydd, who with a liberality peculiarly praiseworthy in so illustrious a prince, had accompanied us from the castle of Aberteivi, throughout all Cardiganshire, to this place, returned home. Having crossed the river in a boat, and quitted the diocese of St. David's, we entered the land of the sons of Conan, or Merionyth, the first province of Venedotia on that side of the country, and belonging to the bishopric of Bangor. We slept that night at Towyn."
The ferry has ceased operating now, but at one stage there were 3 separate ferries, one for coaches and waggons, one for cattle and mounted passengers, and one for foot travellers. I've read that in 1494 the fares were 7s 6d for a coach and four, and 2d for a foot passenger.
A salt refining activity was set up in the 1560s somewhere on the southern side of the Dyfi estuary, using expertise from Germany. The economics of this venture was, as often seems to be the case throughout history, dependent upon external factors and, in this case, the outbreak of yet another fracas with France in 1568. British production was hit and, although subsequently it improved again, there's nothing to suggest that the business ever returned to the Dyfi area. You can read a fascinating and detailed account at: http://www.genuki.org.uk/big/wal/Salt.htmlSpanish Galleon
A Spanish Galleon, supposedly belonging to the Armada, put into the Dyfi on 26 Oct 1597, and a report written by Sir Richard Pryce of Gogerddan, Deputy Lieutenant of Cardiganshire, went as follows: "The Spanish ships which put into Dyfi Haven on October 26th sailed on November 5th. No forces on land could stay her". More was to follow in a report of 19 Nov from Cadwallader Pryce and John Owen, JPs for Merioneth:
"Having received your letter touching the Spanish ship lately arrived in these coasts...we kept in ambush and about ten of the clock in the forenoon eight persons came ashore. They were immediately set upon and two were killed and four taken prisoners. The Spaniards at night moved out of danger of our musketshot and next day, sailed away with the loss of their anchors. They got safe over the Bar leaving us most sorrowful that our care and diligence took not better success."