Blisworth Tunnel has no tow path inside, but is wide enough for two narrowboats to pass in opposite directions. Work began in 1793, but errors by contractor left a wiggle in the tunnel, and after three years work it collapsed due to quicksand, claiming the lives of 14 men. It was then decided to begin again with a new tunnel. By the time the rest of the Grand Junction Canal had opened between London and Braunston, Northamptonshire in 1800, apart from the crossing of the River Great Ouse, the section of canal from Blisworth to the lower end of Stoke Bruerne locks
Netherton Tunnel Branch Canal was later converted to electricity and it is now unlit. The air vents that run along the line of the tunnel and provide ventilation, and a shaft of light into the canal, are known by the locals as "pepper pots", because of their shape. They are brick-lined and the openings are covered by an iron frame or grill. The wide bore and good ventilation mean that boats using the tunnel today are allowed to use the power of their internal combustion engines, which is prohibited in the narrower Dudley Tunnel. The tunnel cost £302,000 as opposed to the £238,000 estimate