The earliest reference to a ship on the Dyfi dates from AD 1109 when the medieval chronicler, Brut y Tywysogion, noted that `Cadwgan and Owen fled into a ship that was lying in the River Dove which had come from Ireland a little while before with exchange in her?.
A survey of ports, creeks and landings places instigated by Queen Elizabeth I in 1569 noted that the Dyfi was a `wonderful greate resorte of ffyshers?.
There are surviving customs records dating to 1641 which provide evidence for the growing importance of the export of lead ore. Corn became an important import to feed the growing local population of lead and silver mine workers (the miners loaded ore onto river boats at Glandyfi to be taken to a large storehouse at Aberdyfi). By the mid 18th century, some 15,000 tons of lead ore or 10,000 tons of lead to the value of £90,000 was being exported annually and Aberdyfi was the fourth busiest Welsh port in terms of receipts and bounties paid on corn. By 1750, the need for a custom controller or port watcher had been well established and Lewis Morris, more well known as a hydrographer and the customs officer at Holyhead, briefly held the appointment.
Samuel Lewis, in his Topographical Dictionary of Wales published in 1833, noted that `the river Dovey is navigable to Derwenlas, within 2 miles of the town (Machynlleth) and affords a facility of conveying the produce of quarries and mines to their destination and of supplying the neighbourhood with various commodities. The average annual exports from this place are 500 tons of bark, 40,000ft of oak timber, 150,000ft of oak poles for collieries; 100 tons of lead ore, and 1500 tons of slate. The average annual imports are 5000 tons of rye and wheat; 1000 tons of coal 500 tons of culm; 2000 tons of limestone and groceries and other ship goods to the amount of £14,000 in value?.
Of the ship yards at Aberdyfi, the first and best facilities were situated at Penhelig. The greatest period of productivity being 1857?1864, during which time 16 vessels were completed.

Sources include:
Association for Industrial Archaeology: A Guide to the Industrial Archaeology of Mid-Wales, 1984
Morgan, D W, 1948, Brief Glory, the Story of a Quest

Maritime Officer, RCAHMW, February 2014.