Lake Baikal is the oldest freshwater lake in the world. In the winter, the lake freezes, but the water is so clear that you can see 130 feet below the ice. In March, frost and sun cause cracks in the ice crust, which results in the turquoise ice shards we see at the surface.
more:
Baikal Treasures. Sapphire sky, turquoise ice by Alexey Trofimov | 500px
lots more:
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