What makes oceans and lakes look blue or green?
Photo: swisscan
When you cup water in your hand, it’s colorless.
You might have heard that a lake is blue because it reflects the blue sky. But the amount of this sort of reflection depends on a number of things, such as your viewing angle. In fact, much of the blue color you see comes from the water’s depths.
White sunlight contains all colors. And water absorbs some of these colors more than others. You need a lot of water to notice this effect, which is why water cupped in your hand has no color at all. In a large body of water, the water molecules quickly absorb red light, but they don’t absorb blue light nearly as well. More blue light is transmitted through the water – so the water looks blue.
Mud acts in the opposite way – it reflects red light more than blue. That’s why muddy water looks brown. The reason the ocean often looks gray on a stormy day is partly because of the reflected gray sky, but it’s also because clouds filter out a lot of the sun’s red light before it ever reaches the water.
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