Karl Johanslussen ("Lock of Charles John") is a lock and a sluice, along the Söderström river connecting and controlling the flood discharge between Riddarfjärden, the easternmost part of Lake Mälaren, and Saltsjön, the section of the Baltic Sea reaching into central Stockholm, Sweden. The lock is 75 metres long, 10 metres wide and 3.90 metres deep. The maximum height is 3.8 metres. The lock is closed from 2016 to 2021 due to large reconstruction works in the area. Before World War I, few of the steam ships in the harbor of Stockholm were larger than 500 tonnes, and the previous lock thus largely sufficient. While commercial traffic was relocated to Hammarbyleden passing south of Södermalm in 1926–1929, the present lock, completed in 1935, was still used by some 3,000 commercial vessels in the 1970s, and log rafts passed through the canal until the 1950s. Its main function is however to allow passage for pleasure boats and sightseeing boats. Construction Like the surrounding area Slussen, named after the lock and built simultaneous to it in 1930–1935, the lock is a concrete construction resting on franki piles (e.g. cast-in-situ piles) located along the sides of the canal and next to the gates. The base plate is made of reinforced concrete, reinforced with steel sleepers next to the gates. The walls of the canal are dressed in granite reinforced with vertical iron rebates stretching three meters from the bottom and horizontal anchoring irons. The two gates are sheeted with steel and lowered from the overhead road bridge, each of them operated with individual machinery hidden in the premises south of the canal. This sort of gates can be operated independent of water pressure, which makes additional aperture and culverts unnecessary for turning the lock. History For historical images, see external links. Following the decline of the military importance of the southern city gate, the area south of the city became the subject for economic exploitation. Sweden was developing into a major power, and as such its capital apparently needed a facelift. The eastern waterfront of the city was remolded into what was to become Skeppsbron, the representative front of the city, and the western part, turned into ashes in the great fire of 1625, was reshaped in accordance to modern town planning. These changes necessarily had to affect the southern city gate and its watercourse; a large slaughterhouse was built on the eastern