Complex sentence: Baikal is home to more than 1,700 species of plants and animals, two-thirds of which can be found nowhere else in the world and was declared a UNESCO World Heritage Site in 1996.
Split into simpler sentences: Baikal is home to more than 1,700 species of plants and animals, two-thirds of which can be found nowhere else in the world. The lake was declared a UNESCO World Heritage Site in 1996.