They are thousands, sometimes even several million years old, or even man-made. They are of impressive beauty and home to hundreds of endemic plant and animal species: Europe’s great lakes. They provide a refuge for animals and humans, are of biological importance, of aesthetic beauty and rich in legendary myths. But these wonderful water worlds are in danger, even though their discovery has often only just begun. Pollution from sewage and waste, overfishing, illegal development. The series captivates with impressive images of nature and shows what solutions are available to preserve these water paradises.