Stock Photo - Lake Titicaca was featured in this image taken by one of the Expedition 8 crewmembers onboard the International Space Station (ISS). Lake Titicaca, at an elevation of 12,507 feet in the Andean Altiplano, is the highest large lake in the world. More than 120 miles long and 50 miles wide, it was the center of Incan civilization, and today straddles the boundary between Peru and Bolivia. Scientists have studied indicators of the water level changes over time to tease out information about precipitation shifts in the high Andes and the South American tropics. Following are some observations by NASA scientists who are studying this imagery: Because the lake occupies the low point of the Altiplano, much of the water of the high plateau eventually trickles into the lake. And because it is surrounded by mountains, very little of Lake Titicaca's water drains out -- the Rio Desguadero is the only major outflow river. So, like a bathtub with no drain, this large and deep lake (with depths of several hundred feet) has become the collecting basin for thousands of years of sediment. These sediments and their fossils contain clues about past climate conditions. The restricted outflow of the lake creates conditions where even shorter, interannual climate cycles (like El Niño Southern Oscillation) impact Lake Titicaca's water levels. Recent lake level variations have been several meters, with low levels occurring during regional droughts of El Niños. Right now, the region is relatively wet. In this image, the dark greens of the wetlands along the shallower margins of the lake contrast strongly with the surrounding desert. But the even large cities like Puno, Peru (100,000 people) are difficult to discern from the surrounding countryside.