Kosa Posolsk (Posolsk Spit) is a kitesurfing spot located on the southeast shore of Lake Baikal, in Buryatia. This sandy spit extending into the lake offers an exceptional setting for kitesurfing on the world's deepest lake.

The water body is vast and open, with very clear and cold freshwater (8-16°C in summer). The sandy beach allows easy launching. On the inner side of the spit, water is calmer and shallower, ideal for learning.

Main winds are the Barguzin (east/northeast wind from the Barguzin valley) and the Kultuk (southwest wind). These thermal winds are often regular in summer. The season runs from June to September. Full wetsuit mandatory due to water temperature.