Complex sentence: By the mid- 1950s very few narrowboats traded south of Napton and the southern section was at one point being threatened with closure, although the northern section (Napton to Coventry) remained well-used by commercial traffic until the 1960s.
Split into simpler sentences: By the mid- 1950s very few narrowboats traded south of Napton. The northern section from Napton to Coventry remained well-used by commercial traffic until the 1960s.