The main line of the canal was completed in 1814, and opened on 9 August. The Welford Arm, which was essentially a navigable feeder, since it connected to the reservoirs which provided the water supply, was not completed until November. The total cost of the project was around £292,000, which rose by another £13,500 the following year. The main line was long, with a level pound of between the locks at Foxton and those at Watford. The opening of the Grand Union Canal provided an additional source of water for the northern summit level of the Grand Junction Canal.