Since March 2014, the Knappensee (Hórnikečanski jězor) has been closed to allow the long-term planned bank consolidation work to be carried out. According to the original plan, the renovation work was to be completed in 2017. After a delay, it was scheduled to be completed in the course of 2022.
A large-scale landslide on March 11, 2021 delayed the 2022 planning target again. In an unrehabilitated section in the northeast of the Knappensee, there was a large-scale subsidence flow. The bank slope slid into the lake over a length of 400 to 500 meters. The affected area extended up to 200 meters into the hinterland. The previous tree cover was also torn into the lake. The landslide triggered a 1.5 meter high flood wave, which caused damage in a bungalow settlement opposite in Groß Särchen. The water level rose by 36 centimeters that day, and the amount that flowed out is estimated at around 1 million cubic meters. Now (as of July 1, 2022), necessary renovation work is scheduled to be completed by the end of the 2020s before the lake is reopened for use.
Until it was closed, the lake was a popular sports water. There were several sailing clubs, a canoe club and a lake sports club on the shore. The approximately 8-kilometer-long circular path around the water was used by many runners as a training route. In addition, the Knappensee had several campsites and opportunities for permanent camping. It was a popular local recreation area for the city of Hoyerswerda.