In 1919 the pond is excavated. The plan is to make a large round pond that becomes a small waterway. But the oxidized iron layer in the ground is damaged during the excavation work. Normally, the iron layer prevents the rainwater from seeping away, but now the pond runs empty time and again. After countless attempts to repair it, an artificial bottom is installed with rolls of mastic (asphalt), which are rolled out across the entire floor of the pond and attached to each other with tar. The bottom has been waterproof ever since.