The Cottbuser Ostsee Halbmarathon – Ostsee Run is an evening road race held in Cottbus, Brandenburg. The start and finish area are located in Willmersdorf. Participants can select between a half marathon, a 10 km run, or a 5 km run. Additionally, Nordic walking and walking options are available, allowing non-runners to participate in the event program. This race is part of the Niederlausitz-Cup and was established in 2021, making it a relatively new addition to the regional race schedule.
The half marathon route follows the Cottbuser Ostsee, a substantial lake area situated on the outskirts of Cottbus. The event is also known by the name Ostsee Sportspiele. It is organized by SG Willmersdorf e.V. and Teichlandradler e.V., contributing to a local club atmosphere rather than a large-scale marathon event. Teichlandradler also engages in cycling activities around the Cottbuser Ostsee, the Neiße region, and the Spreewald, indicating the race's integration within a wider local outdoor sports community.