Just outside the town of Wagrowiec, in the Paluki region of Poland, two rivers cross at a right angle and the waters of each go their own way without mixing. This rare phenomenon occurs nowhere else in Europe and in only one other place in the world.

The Welna and Niebla rivers meet at a concrete weir, installed in the 19th century, where the bodies of water go into a whirlpool motion that keeps the two streams separate before continuing on their way in their own riverbeds. Only 10 to 15 percent of the waters mix during this time.

It seems appropriate this unique watery wonder be found in Paluki, which is nicknamed “the land of 130 lakes.” The surrounding area must be flat for the phenomenon to occur, and the weir was installed amid the region’s farmland as part of a deliberate manipulation of the two rivers to improve farming conditions in the area. The town wanted to streamline the flow of the Welna to make it more helpful with local irrigation and reduce flooding. The strategy was to cross it with the Niebla, a smaller river that was redirected south to help relieve the Welna of surplus water.

Further west, the rivers cross paths again, this time joining each other on their way to Legowskie Lake. Analysis of the biological content of the waters of both rivers on both sides of the crossing have shown that they remain mostly the same from before the bifurcation to the second meeting as they approach the lake.