The IJmuiden locks form the connection between the North Sea Canal and the North Sea at IJmuiden. The lock complex consists of the Zuidersluis from 1876, the Middensluis from 1896, the Noordersluis from 1929, the Spuisluis from 1940, and the Gemaal from 1975. To the west of the locks is the Fort Island, part of the Defense Line of Amsterdam. In 1859, the Water Management Board came up with a plan to make the large lock 140 meters long, 18 meters wide and 7.75 meters deep and the small lock 70 meters, 12 meters and 5 meters. Most ships of that time could pass the large lock without much problem. In 1868 the length of the large lock was reduced to 120 meters. Excavation work was completed in the spring of 1871 and the locks in the fall of 1872. The walls of the lock were brick, the floodgates of wrought iron and the ebony doors of pinewood. After the official opening, it soon became clear that the Zuidersluis was too tight. Ships of 150 meters and longer came into service and they did not fit in the lock. The pumping station on the other side of the canal, near Schellingwoude, also failed. During the discharge, the two locks could not be used for shipping, which reduced the capacity even more. In 1885, less than 10 years after its opening, a first design for a third, larger lock was submitted. This lock would be 205 meters long, 25 meters wide and 8.50 meters below NAP. On May 31, 1887, the government approved the construction and, learning from the first experience, it was decided to increase the length to 225 meters and the depth to 10 meters.