The lake was created by flooding the former Tagebau Zwenkau coal mine, which operated until 1999.
Kap Zwenkau houses a distinctive architecture piece known as the 'Pier 1', which includes an observation tower.
The reservoir has a water volume of approximately 175 million cubic meters.
It is connected to the river Pleiße via the Zwenkauer See-Kanal, though navigation is restricted to non-motorized vessels in specific zones.
The lake basin contains several artificial islands created to provide habitats for local bird species.
Cossi, locally known as Zwenkauer See, is a former open-cast lignite mine transformed into a 5.7-square-kilometer lake. It serves as the largest body of water in the Leipzig New Lakeland district. The lake features a modern marina, Kap Zwenkau, which functions as a central hub for nautical tourism. The basin reached its final water level in 2015 after a decade-long flooding process. Its depth reaches up to 55 meters in certain sections. The area is integrated into an extensive network of cycling and walking trails surrounding the southern Leipzig mining landscape. Water quality is monitored regularly and currently supports regulated swimming activities.
The observation deck atop the Kap Zwenkau main building offering a panoramic view of the lake surface.
Rent a bicycle to traverse the 22-kilometer perimeter path that connects to the surrounding forest areas.
Check the official water quality bulletin board at the main beach entrance before entering the water.
Visit the pier area during weekday evenings to avoid the peak crowds of the weekend leisure traffic.
Attempting to swim in non-designated zones or near the industrial harbor docks where boat traffic is active.
The lake is accessible year-round, though swimming is generally restricted to the official summer season.
Maintain noise levels near the residential sections of the harbor; observe designated zones for swimming versus motorized boating.
