The whole length of 16.5 miles (26.6 km) was completed by October 1798. Civil engineering works included 36 locks and five aqueducts to carry the canal across major tributaries of the Afon Tawe, at Clydach, Pontardawe, Ynysmeudwy, Ystalyfera, and Cwmgiedd.
The canal had one curious feature: a central section just over a mile in length, was a private canal built by the Duke of Beaufort, which ran from Nant Rhydyfiliast to Nant Felin, on which the Duke was allowed to charge tolls. The Duke's section was called the Trewyddfa Canal, but was part of the main line.
The locks on the main section were 69 by 7.5 feet (21.0 by 2.3 m), but those on the Duke's section were only 65 feet (20 m) long, and this restricted the maximum length of boats. The locks raised the canal from near sea level at Swansea through 373 feet (114 m) to reach Abercraf.
At Swansea, wharfs were built alongside the river, where cargo could be transhipped into coasters. Unusually for such projects, the final cost was well within budget, with the project costing £51,602 up to mid-1798.
The opening of the canal caused an increase in industrial activity along the valley, with a number of manufacturing companies setting up works by its banks. Four short branch canals were constructed, and a network of tramways gradually linked mines and quarries to the canal.
There are few records of how much traffic was carried, but estimates based on the amount of coal and culm shipped from Swansea Docks suggest around 386,000 tons in 1839. The opening of the Tennant Canal to Swansea Docks in 1824 resulted in the Swansea Canal's riverside wharfs being improved.
The canal was bought by the Great Western Railway in 1873 for a price of £107,666 for the main Swansea Canal, and £40,000 for the Duke of Beaufort's Trewyddfa Canal and continued to be profitable until the mid-1890s. The last commercial traffic was in 1931, boats continued to operate on the canal after that date but only for maintenance work, with horse-drawn boats last recorded at Clydach in 1958.
Decline
In-filling of much of the canal has taken place in the past 50 years. The northern section was affected by the creation of the A4067 road around Ystradgynlais, while the southern section below Clydach had been infilled by 1982. In October 1998, after heavy rainfall a breach caused extensive flooding at Pontardawe, thirty houses, some industrial units and town centre shops were affected, with the water up to 4 feet (1.2 m) deep in places.
Restoration
In 1981, the Swansea Canal Society was formed, and have been working towards restoration of the remaining sections of the canal. They have done much to improve the physical environment of the canal. A project is underway to dredge the canal and to remove the Japanese knotweed that grows extensively around the Swansea Valley.
