"The Peyto Glacier once filled this valley. Now it is merely a tongue of the larger Wapta Icefield. Yet you can see proof of the glacier's former presence. Past glacial advances gouged out the U-shape of the valley and the bowl of the lake. This glacier is one of the best studied glaciers in the Canadian Rockies. The recent discovery of 3000-year-old wood fragments covered by the ice indicates that much of what is now glacier was once forest. But advances and retreats are part of a glacier's life. The glacier has receded about two kilometers in the last century.
Why is the lake blue? The junction of the stream, the lake and the delta is the clue. Water leaving the glacier is muddy with rocks, gravel and silt. As the stream slows down most of that rubble is left behind to become delta. Silt flows into the icy water where most of it sinks to the bottom. Fine particles of rock ground to the texture of baking flour remain suspended in the water. This "rock flour" scatters the blue-green rays of light, giving the lake its special color.
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