Crater Lake, Oregon.
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Crater Lake, Oregon is the deepest lake in N. America and the 5th deepest in the world. Containing only rain water and melted snow it reflects the blue spectrum color from the sunlight to provide a wonderful deep blue.
The day we visited there was a heavy smoke haze from a nearby forest fire. It meant the full sunlight could not penetrate the water. But the blue from the water was still stunning. With a calm wind the reflections of the crater walls along with Phantom Ship island made a perfect, if slightly hazy, image.