When the Glynneath bypass was built in the 1970s, the canal was culverted above Ysgwrfa lock, to allow the road to be straightened, and reduced in width beyond that, to allow the road to be widened. Above Pentremalwed lock, the road was built over the canal bed, and all traces have gone. This road was superseded by the A465 dual carriageway when it opened in 1996, and has become the B4242 road. The part which covered the final section of the canal is no longer a road, although the dual carriageway runs over the site of the Glynneath basin.