Masurian Canal

The unfinished Masurian Canal begins in Mamerki.
Connection between the Masurian Lakes and the Baltic Sea, never completed.
More information: pl.wikipedia.org/wiki/Kana%C5%82_Mazurski

The Masurian Canal (German Masurischer Kanal, Russian: Канал Мазурский) - an unfinished water channel, which was to connect the Great Masurian Lakes with the Baltic Sea through the Łyna and Pregoła rivers. Currently, the Masurian Canal runs through the territory of two countries: Poland and the Russian Federation. It is not open to shipping.
The project to build the Masurian Canal, which was created at the end of the 19th century, was based on the earlier works of the Polish brothers who settled in Duchy of Prussia. In the 17th century, Józef Naronowicz-Naroński developed detailed maps of the lakes and the plan of connecting the Pregoła River with the Nemunas through the canal, and the continuator of his work, Samuel Suchodolec (Suchodolski), developed a design of the canal to connect the lake with the Nemunas. Śniardwy with the lake Niegocin and further with the Pregoła River.
Along with the construction of canals between the Masurian lakes, which began in 1764, the idea of connecting them with the Baltic Sea through a new canal began to be increasingly considered. From among several possible variants, the route connecting Lake Mamry with the Łyna River was selected as the most economically justified. The design of the canal, approx. 50 km long, with 6 barrages and a slope of approx. 111 m, was developed in the years 1849–1862. However, it was not implemented. Another project, which was developed in 1874, was already approved by the National Parliament of East Prussia, but due to problems with land ownership along the route of its construction, it was also not implemented. In the years 1890–1898 an attempt was made to implement another version of the project. It assumed the construction of locks instead of the previously proposed slipways, and the construction of hydroelectric power plants was planned at individual steps of the canal (there were to be 6). Two security gates in the form of cylindrical weirs were also designed. This concept was also not implemented, mainly due to the protests of the inhabitants of the Pregoła and Deja valleys fearing an increase in the risk of flooding. There were also concerns that the planned constant water supply to the canal in the amount of 6 m³ / s would result in difficulties in navigation (especially in summer).
pl.wikipedia.org/wiki/Kana%C5%82_Mazurski

The beginning of an unfinished building.