Secret Life of Lakes

Our planet's lakes make up a huge and precious freshwater reserve from which mankind has drawn for tens of thousands of years. Created by a wide range of climatic and geological conditions, these lakes are maintained through the delicate balance between the water that feeds them and the rivers into which they drain. Although all lakes may seem alike, they are extremely diverse. Some are as deep as oceans; others can be crossed almost without getting one's feet wet. Certain lakes seem like they will be here for an eternity while others come and go with the seasons. But they all have one thing in common: they are all home to rich and varied life forms in their depths and on their banks. (Viasat)