Lake Baikal rules the worldly superlatives: deepest lake (5400ft/1600m), largest by volume (contains ~20% of the world’s surface freshwater) and home of the only exclusively freshwater seal. Formed within a rift valley, the lake is around 25 million years old and lies among the coniferous forests of south-central Russia.
Here is the annual melt, with this imagery from March 9, 2020. I’m curious what causes the streaking in the top image; my guess is that this is fractured and partially submerged or waterlogged ice. Among interesting features observed from space are strange circular holes in the ice, first observed by astronauts. The lake is also the only known freshwater body to feature gas hydrates emitted from submerged mud volcanoes (which form bubbles locked in lake ice in the winter). If you are especially keen, read up on the region’s glaciological history here—it’s also pretty cool…
Satellite data from ESA’s Copernicus program. CC BY-SA 3.0 IGO.