Why do some lakes appear bright blue or emerald green?

Pure water absorbs more red and orange light than blue, so large deep lakes often look blue when sunlight penetrates them. If the lake contains fine sediment, algae, or dissolved minerals, the reflected color can shift toward green or turquoise. Glacier-fed lakes often owe their vivid color to suspended rock flour, while algae-rich lakes may look greener. The angle of sunlight and the depth of the water also affect the appearance. That is why lakes can seem to change color during the day or across seasons.