There are other factors that can affect our perception of the color of water. For example, particles in water can absorb light, scatter light, and reflect light. Light may be absorbed by particles and solutes, as evidenced by the darker color of tea or coffee. Green algae in rivers and streams often lends a blue-green color to the water. Some mountain lakes and streams that contain finely ground rock, such as glacial flour, are turquoise. The surface of water can also reflect skylight.