Nowadays, the countryside from Tri-Nation Point to Kristýna is changed due to the lignite mining that took place in several stages since the end of the 18th century. There used to be three lakes in the area between Tri-Nation Point and Hrádek on the right bank of the Nisa River before opening the first shafts. The river looked also different – it curved in many meanders. The river was led to today’s straight river-bed only in the 1930s in connection with expansion of the lignite mining. Dozens of shafts, where the miners were getting the lignite from, were built in the area between Žitavská ulice (Zittau Street) and the river since the end of the 18th century. During the mining, the miners were constantly fighting a lot of groundwater. The today’s marshland is also the remains of the mining. Next to the marshland there is a meadow which was created by the landfill reclamation. The landfill was in an area originally used for mining too.
The biggest shaft Christian was named after Kristián Kryštof or Kristián Filip Clam-Gallas, who owned Grabštejn and therefore all the mining shafts. The underground mining was changed to the surface mining in 1952. It continued until 1972, when the mining was finished. Today’s Kristýna Lake is the most visible remain of the mining times in Hrádek nad Nisou.