Overview: Japan's biggest lake: Lake Biwa. It is 4 million years old, a source of water for 14 million people, and home to over 10 aquatic creatures that are only found there. Lake Biwa contains rare freshwater pearls, its scenic landscape has captivated artists for centuries, and it also has spiritual significance. The lake's ecosystem has been threatened by water pollution and the introduction of invasive species, but locals have come up with some creative ideas to reclaim the environment.