Its second objective was to allow the free passage of ships. This required the construction of two sluices in Przegalina – one for small rafts, the other for shipping. In the second half of the 20th Century the sluice for small boats was renovated and turned into another shipping sluice, which was given the name of the Southern Sluice. The previously-larger sluice (northern) was closed and has been a historic site ever since.
The historic northern sluice has a concrete and wooden structure, while the walls of the heads of the sluice are brick. The first of the two pairs of gates were to protect from floods, while the other served as daily-use gates. The system of propelling the sluice was situated in a nearby building. It still features the original late-19th-Century devices.The new Southern Sluice is currently the only active sluice for ships to pass between the Vistula and the Martwa Wisła.