Morfydd Street Turnbridge on the Trewyddfa Canal was built c. 1794-6 as one of the original structures of the Swansea Canal. Rubble sandstone with primitive copper slag string course, rubble voussoirs and slag copings. The bridge is complex in structure, consisting of two crossings of the canal at the same point. The bridge was extended during the mid-C19 to the west, carrying Morfydd Street over a railway branch.

This is the most southerly visible structure associated with the Swansea-Trewyddfa Canal line other than the entrances to the Hafod Copperworks Docks and the limekiln opposite them (a survivor of some 60 built along the canal). It stood near the northern end of the Trewyddfa Canal as the canal's towing-path from Landore to Morriston was uniquely on the hill-side of the canal to allow unrestricted access to the waterway to the four pre-existing copperworks situated on the riverside (towing-paths were in this position on all the valley canals in order to utilise the necessary water-retaining bank constructed on the lower, or river, side). It differs from the other nine overbridges surviving on the on the line of the Swansea and Trewyddfa Canals in that it was a turnbridge, but, like them, it was built of coursed rubble-stone with parapets formed of rectangular cast copper-slag blocks. As a turnbridge it has an additional curved track on its northern side to accommodate the towing path as it crosses the canal. Two other turnbridges (also known as roving bridges) stood on the Trewyddfa/Swansea Canal line south of this point.

Initially the Trewyddfa Canal was built as a 30 ft. (9.l m) wide waterway flanked by 8 ft. (2.4 m) wide towing-paths on both sides.1 To the north it ran on the valley or eastern side. Towing-paths were in this position on all the valley canals in order to utilise the necessary water-retaining bank on the valley side rather than having to go to the expense of cutting a towing-path into the scarp above the canal.

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l. Badminton. Group.II. MSS., 2134 (NLW).