There was no immediate pressure to extend the canal to Giant's Grave, as access to Neath for coastal vessels of up to had been improved in 1791 by the construction of the Neath Navigable Cut. However, a second Neath Canal Act was passed on 26 May 1798, to authorise an extension of about to Giant's Grave, where better facilities for transferring goods to seagoing vessels were available. Thomas Dadford again surveyed the route, but Edward Price from Gofilon acted as engineer. This part of the canal was financed by Lord Vernon, although he was also paid £600 for his Penrhiwtyn canal, which became part of the main line. The extension was completed on 29 July 1799, and terminated at a basin close to Giant's Grave Pill. Flood gates on the canal enabled water to be released into the pill to scour it of silt. The total cost of the project was about £40,000, which included 19 locks and a number of access tramways. Between 1815 and 1842, additional docks and wharfs were built at Giant's Grave, extending the canal slightly, and the canal was extended to Briton Ferry by the construction in 1832 of the Jersey Canal, which was about long, and was built without an Act of Parliament by the Earl of Jersey. Another short extension was made around 1842. The final length of the canal was .