Why does water look blue or green when it's in large bodies of water instead of some other color?

Answer 1

Because water (and particles in it) is reflective and large bodies of water are maily covered by sky, not trees... so it reflects the blue of our atmosphere.

It's green when its "dirtier" water reflecting the blue, dark blue at night, and greyish when it's cloudy.

ps- One of the main causes of scattering is due to the reflection of radiation (in this case, light) and it's angle. This is also called diffuse reflection.

Answer 2

well.....It seems that a combination of the preceding answers would be better to completely answer the question:

Since The light source is out of the water, reflection AND refraction must be taken into account; sky looks blue (and its explained why, thanks), if you remember some underwater footage; if camera is looking up to the surface you'll realize that water is not blue by its nature, no matter how much organism or mineral are there, but downward? it looks dark blue right? which shows us that, since there is no source down there sunlight reaching the deep reflects to you/camera in blue.(same event as atmosphere). but same doesn't stands for green rivers.

For rivers with high flow rate, one may claim that the color comes from the ingredients-organisms and so on, which won't be false, but for rivers with low flow rates or lakes? for still water(and slow also), one can take gravity in to account and easily see that there won't be that many ingredient if compared, especially around surface. where we need reflection to explain the color. Around this water source of ours, probably is a large flora. and if water is very very still we can even see the mirror image of the surrounding on the surface, well stir it a bit, add some flow if you like, there is the green! okay okay, a bit more serious example: recall a night view of a city at the shore, the sea would be of all the colors of the city lights, right? now our light/color source would be the woods around......that's all!

P.S. surely dirty brownish rivers are self-explanatory... :D

Answer 3

None of the previous 2 answers is correct. While water can reflect, that's not the main reason that it is blue/green. But it is blue or green for the same reason that the sky is blue. Higher frequency colors (like blue, green) collide with more molecules than lower frequency colors like red or yellow. So when light goes into the water, bluer frequencies tend to "scatter" more and thus that's why you seem them more than other colors.

This also explains why sunsets are usually red/yellow. When the sun sets way to one side of the earth (from the observer's perspective), it has to go through much more of the atmosphere compared to when the sun is directly over head. So even the red/yellow frequencies scatter when they go through longer stretches of the atmosphere/air.

Answer 4

Large body of water reflects the color the sky. However, there are micro organism that live in the surface of the water body that can affect that by altering it to different shades of blue.