Lakes are bodies of water not connected to the ocean. Most contain fresh water, which makes them a focus for life, as all land-based animals require fresh water to survive. Just 3 percent of the world’s water is fresh, with two-thirds being locked away in polar or glacial ice. Lake Baikal and the Great Lakes make up as much as half of what’s left over. We look at the way Russians make use of their lake during the winter when it freezes over, and the effect on global warming when the lake starts to thaw, releasing methane and carbon dioxide from the thawing process.