straddling the border of bolivia and peru, lake titicaca boasts the most beautiful lake in the world. for those who live nearby, it's more than a scenic wonder. water is essential to the very existence. those waters are rapidly disappearing. >> reporter: it's the largest lake in south america and it's at risk. located at 3,800 meters above sea level on the border of bolivia and peru. lake titicaca has sunk to the lowest level in 60 years, evaporating two to three centimeters a week. global warming is to blame. and the length of the rainy season has been cut in half. >> translator: where we are standing, this time last year, it was covered by water. thousands of birds were feeding from it. now, as you can see, it's completely dry. >> reporter: millions of people depend on the lake and they have already started to feel the consequences of the disappearing waters. this man was forced to move his cattle to be nearer the water. the area they once came to drink is now dry and abandoned. >> translator: as the climate changes, little by little, we are forced to go with our animals to where th