Taken at Peyto Lake in the Banff National Park, Alberta,Canada.
The lake really does look this green as it is glacier fed and it is caused by Rock flour.
Rock flour, or glacial flour, consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion
When the sediments enter a river, it turns the river's color gray, light brown, iridescent blue-green, or milky white. If the river flows into a glacial lake, the lake may appear turquoise in color as a result.