Lake Baikal Day is observed in Russia every first Sunday of September, dedicated to the conservation of Lake Baikal, the world’s largest freshwater lake by volume, located in southern Siberia between Irkutsk Oblast and the Buryat Republic. The holiday originated in 1999, initially celebrated on the fourth Sunday in August, and was later moved to its current date in 2015. It has grown from a local observance in Irkutsk to a nationwide celebration. On this day, Russian environmental organizations conduct various events, including lectures, seminars, exhibitions, and film festivals, to educate the public about the unique ecological significance of Lake Baikal and the importance of its preservation. Lake Baikal is not only the deepest and oldest lake in the world but also home to numerous endemic species, and it was declared a UNESCO World Heritage Site in 1996.