There's a lake that's a million years old and has no outlet - Apparently.
Lake Baikal in southern Siberia, Russia, is the world's largest and oldest freshwater lake, with approximately 20% of the world's unfrozen freshwater. It's estimated to have formed around 25 million years ago, but its bedrock is thought to be around 1 million years old, with some areas dating back to the Paleogene period. Despite its vast size, Baikal has no outlet to the ocean and is home to over 2,500 species of plants and animals, many of which are found nowhere else in the world.