Blisworth Tunnel was the only section unfinished. This was despite the tunnel having been under construction for seven years: the gap was filled by a temporary horse-drawn tramway over the top of the hill, with goods being transported from boat to wagon and back again. The tramway, built in 1801, was Northamptonshire's first railway. In March 1805, the tunnel was finally opened and the rails were used to connect the main line of the canal to the River Nene until the branch canal to Northampton was constructed. Until the 1870s travel through the tunnel was only achieved by men lying on their
Shrewley Tunnel which crosses the tunnel; having crossed this the path then descends on another ramp to reach the southern portal. The interior of the tunnel is unusually wet and this has led to the creation of flowstone formations. The tunnel runs from the south-east to the north-west. From the northern portal, the canal is level for to the bottom of a flight of five locks at Knowle, which raise the level of the canal by . Kingswood Junction, which connects to the Stratford-upon-Avon Canal occurs about halfway along this stretch. To the south, the canal if level for around to Hatton