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How Can Bodies of Water Be Different Colors?

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When I saw the Caribbean Sea in person for the first time, my eyes metaphorically popped out of my head. As a kid who grew up in South Jersey, I was used to the dirty, almost brown, kinda-sorta blue color of the coastal Atlantic Ocean. But this was different. Staring at that bright, vibrant, and seemingly crystal-clear water, I had many questions. Where did that color come from? And why can I see my feet here, but not at home? Is the Caribbean water cleaner? Is the sun stronger down south? And how come it’s green-blue near the shore, yet navy blue a mile off shore?

Having traveled quite a bit since, I’ve heard all kinds of explanations from common folks, some chalking color differences up to pollution and others to salinity. While I’m certain that many factors, including those two, play some small role, the biggest influencers are the floor, depth, and microorganisms of the body of water.  

First off, let’s tackle why water, in most cases, appears blue to begin with.

Shedding a little light

If you’ve ever taken a cruise, you know that the farther offshore you sail, the deeper and bolder the blue becomes (navy blue). That’s because there are no reflections off the sea floor in very deep water, meaning that a majority of the sun’s rays are absorbed by the water itself. Water molecules, by nature, absorb reds, greens, oranges, and yellows, but spit out blue.

“When sunlight hits the ocean, some of the light is reflected back directly but most of it penetrates the ocean surface and interacts with the water molecules that it encounters,” explains NASA’s Oceanography Division. “The red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light we see is composed of the shorter wavelength blues and violets.”

Sanding Off

As the water depth decreases and the light is able to penetrate all the way to the bottom, the makeup of the floor becomes a factor in determining water color. For example, the coarse Caribbean coral is going to reflect light differently than the fine sand found in the Northeast. These differences in absorption and reflection affect visibility as well as color.

Whatever light is not reflected back from the top layer of water or the bottom of the sea floor is absorbed by something in the water. As we saw above, lots of light is consumed by the water molecules themselves, but microorganisms living in the water also “eat” their fair share. The final major players in determining color are the particles and organisms found and suspended in the water. Phytoplankton, for example, harbors chlorophyll that absorbs red and blue light and reflects green. If a high concentration exists in one area, the water will take on a green hue. The more there are, the greener the water will appear.

Those three factors—depth, floor makeup, and life (plus intangibles, like pollution, as mentioned above)—will interact to produce whatever color we happen to see. The same principles apply to other bodies of water, like lakes, craters, and rivers. It’s all about what’s in and under the water.

And, despite our focus on the oceans, it’s not all about being green, blue, or brown. Check out these uniquely colored tourist attractions found in different parts of the world as examples. If you thought the greenish-blue of the Caribbean was impressive, the red and black volcanic lakes should knock your socks off.

Laguna Colorada, Bolivia

Courtesy of Flickr user Valdiney Pimenta

Red sediments and algae pigmentation produce the unique red color of this salt lake in Bolivia, which is further contrasted by the white borax islands that are spotted throughout it. Located at more than 13,000 feet above sea level, the lagoon is part of the Andean Fauna National Reserve and is a common roosting spot for a variety of flamingo species.

Kelimutu Volcano, Indonesia

Courtesy of Flickr user NeilsPhotography

This volcano harbors three crater lakes at its summit that are strikingly different from one another in terms of color. Typically, Tiwu Ata Mbupu (Lake of Old People) appears blue, Tiwu Nuwa Muri Koo Fai (Lake of Young Men and Maidens) green, and Tiwu Ata Polo (Bewitched or Enchanted Lake) either black or red, although they all are known to change shades quite frequently and unpredictably. The latter two are separated by a crater wall, creating a stunning distinction when viewed side-by-side, especially when they are green and black, as seen in the photo. Thus far, research has revealed no official explanation for the differences and changing colors, but the general consensus is that chemical reactions are being triggered by volcanic gas activity that drives nutrient-rich water to the surface.

Lake Pukaki, New Zealand

Courtesy of Flickr user Peter Nijenhuis

Glacial erosion fills this body of water with glacier flour, or finely-ground rock particles, resulting in a frosty, cloudy-blue color (this mixture is sometimes referred to as glacial milk). Lake Pukaki has a surface area of approximately 111 square miles and was formed when glacial debris known as moraine dammed up the valley. There are glacier lakes in at least a dozen countries throughout the world that take on this “milky” appearance. While they are not abnormally colored, the Great Lakes are the largest glacial lakes in the world.

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Big Questions
Can You Really Go Blind Staring at a Solar Eclipse?
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A total solar eclipse will cut a path of totality across the United States on August 21, and eclipse mania is gripping the country. Should the wide-eyed and unprotected hazard a peek at this rare phenomenon?

NASA doesn't advise it. The truth is, a quick glance at a solar eclipse won't leave you blind. But you're not doing your peepers any favors. As NASA explains, even when 99 percent of the sun's surface is covered, the 1 percent that sneaks out around the edges is enough to damage the rod and cone cells in your retinas. As this light and radiation flood into the eye, the retina becomes trapped in a sort of solar cooker that scorches its tissue. And because your retinas don't have any pain receptors, your eyes have no way of warning you to stop.

The good news for astronomy enthusiasts is that there are ways to safely view a solar eclipse. A pair of NASA-approved eclipse glasses will block the retina-frying rays, but sunglasses or any other kind of smoked lenses cannot. (The editors at, an eclipse watchers' fan site, put shades in the "eye suicide" category.) NASA also suggests watching the eclipse indirectly through a pinhole projector, or through binoculars or a telescope fitted with special solar filters.

While it's safe to take a quick, unfiltered peek at the sun in the brief totality of a total solar eclipse, doing so during the partial phases—when the Moon is not completely covering the Sun—is much riskier.


NASA's website tackled this question. Their short answer: that could ruin their lives.

"A student who heeds warnings from teachers and other authorities not to view the eclipse because of the danger to vision, and learns later that other students did see it safely, may feel cheated out of the experience. Having now learned that the authority figure was wrong on one occasion, how is this student going to react when other health-related advice about drugs, alcohol, AIDS, or smoking is given[?]"

This story was originally published in 2012.

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Big Questions
If Beer and Bread Use Almost the Exact Same Ingredients, Why Isn't Bread Alcoholic?
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If beer and bread use almost the exact same ingredients (minus hops) why isn't bread alcoholic?

Josh Velson:

All yeast breads contain some amount of alcohol. Have you ever smelled a rising loaf of bread or, better yet, smelled the air underneath dough that has been covered while rising? It smells really boozy. And that sweet smell that fresh-baked bread has under the yeast and nutty Maillard reaction notes? Alcohol.

However, during the baking process, most of the alcohol in the dough evaporates into the atmosphere. This is basically the same thing that happens to much of the water in the dough as well. And it’s long been known that bread contains residual alcohol—up to 1.9 percent of it. In the 1920s, the American Chemical Society even had a set of experimenters report on it.

Anecdotally, I’ve also accidentally made really boozy bread by letting a white bread dough rise for too long. The end result was that not enough of the alcohol boiled off, and the darned thing tasted like alcohol. You can also taste alcohol in the doughy bits of underbaked white bread, which I categorically do not recommend you try making.

Putting on my industrial biochemistry hat here, many [people] claim that alcohol is only the product of a “starvation process” on yeast once they run out of oxygen. That’s wrong.

The most common brewers and bread yeasts, of the Saccharomyces genus (and some of the Brettanomyces genus, also used to produce beer), will produce alcohol in both a beer wort
and in bread dough immediately, regardless of aeration. This is actually a surprising result, as it runs counter to what is most efficient for the cell (and, incidentally, the simplistic version of yeast biology that is often taught to home brewers). The expectation would be that the cell would perform aerobic respiration (full conversion of sugar and oxygen to carbon dioxide and water) until oxygen runs out, and only then revert to alcoholic fermentation, which runs without oxygen but produces less energy.

Instead, if a Saccharomyces yeast finds itself in a high-sugar environment, regardless of the presence of air it will start producing ethanol, shunting sugar into the anaerobic respiration pathway while still running the aerobic process in parallel. This phenomenon is known as the Crabtree effect, and is speculated to be an adaptation to suppress competing organisms
in the high-sugar environment because ethanol has antiseptic properties that yeasts are tolerant to but competitors are not. It’s a quirk of Saccharomyces biology that you basically only learn about if you spent a long time doing way too much yeast cell culture … like me.

This post originally appeared on Quora. Click here to view.


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