Why is Caribbean Water so Clear and Blue?

When visiting a beach destination in the Caribbean you may wonder why the water is so incredibly clear and beautiful. Some describe the water as blue, azure, cerulean or just blue/green. Regardless, most people would agree that it’s absolutely breathtaking. After years of wondering, I decided to find out for myself why the waters of the Caribbean are so beautifully clear and blue.

The Caribbean sea is so clear and blue because has little presence of plankton – or other substances – and it’s relatively shallow so most of the light is reflected. As a result, we see beautiful clear blue water. Water gets its color from the interaction of sunlight with water and the substances in the water.

OK. So I oversimplified the whole operation so let’s dig a little deeper…

Exactly Why is the Caribbean Sea so Clear and Blue?

As I mentioned, The color of the ocean water is determined by the interaction of sunlight with substances in the water.

Interaction of sunlight affects the color of water

Sunlight is made of an array of colors that appears to us as white. When it hits the water it’s broken apart by water droplets into a rainbow of colors.  The colors are transmitted and either absorbed, scattered or reflected by the water in a variety of shades and hues.

  • The light that is absorbed is pulled in by the water and transformed into heat energy. Deeper waters absorb more.
  • Scattered light bounces off the surface into different directions than where it came from. Blue wavelengths of light are scattered at different angles resulting in varying shades of blue.
  • Reflected light bounces off the surface into a single direction from where it came from.  Much of the ocean’s blue color is a reflection of the sky above.

Red, orange, yellow and green wavelengths of light are primarily absorbed (vs. scattered or reflected) and blue wavelengths reflected, which is the main reason the ocean is primarily blue.

Substances in the water affect the color of water

The substances beneath the water are primarily free-floating plankton but can be any number of other suspended particles. These substances increase the scattering of light so less light is reflected.

Plankton uses a green element called chlorophyll in order to produce carbon via photosynthesis. Since plankton prefers to absorb red and blue portions of the light spectrum it then reflects green light vs blue. In other words:

  • High amounts of plankton result in a greener appearance
  • Low amounts of plankton result in a bluer appearance.

Admittedly, this is my translated version. If you want to geek out on the details check out this NASA Science article.

Why are some ocean waters murky and brown?

Most of the sunlight that hits the ocean is absorbed, especially in the deepest areas. Deep ocean water has no reflection of the seafloor so red wavelengths are absorbed and water appears dark.

However, in coastal areas, the water can also appear dark. And it can also look murky and brown. This is because there are more substances such as plankton, silt, other particles and even living organisms (ocean animals) floating around causing water to appear cloudy.

In contrast, mountain lakes and streams often appear crystal clear due to the absence of suspended particles.

Where is the clearest water in the Caribbean?

It was a bit more difficult to find agreement on the clearest waters in the Caribbean. Of all the incredibly nominees I came across, I selected the top 5 that appeared in travel experts’ lists the most.

Exuma, Bahamas was included in this list but I omitted it since it was included in the above “worlds” clearest waters list.

  1. Shoal Bay, Anguilla
  2. Trunk Bay, St. John
  3. Seven Mile Beach, Grand Cayman
  4. Galley Bay, Antigua
  5. Marigot Bay, St. Lucia

Shoal Bay, Anguilla

Gorgeous clear blue waters of Shoal Bay, Anguilla


Trunk Bay, St. John – US Virgin Islands

Take a dip in these clear blue waters in Trunk Bay of St. John


Seven Mile Beach, Grand Cayman

Amazingly clear blue water on Seven Mile Beach on Grand Cayman Islands


Galley Bay, Antigua

Crystal clear blue water of Galley Bay in Antigua


Marigot Bay, St. Lucia

Marigot Bay’s version of clear blue water in St. Lucia


The absence of plankton gives us beautiful clear blue Caribbean waters. But what about sea life?

I wanted to circle back to the topic of plankton since it’s such a major factor in why the Caribbean waters are so clear and blue.

In my research, I learned that plankton is essential for sea life survival. According to the Oceanic Research Group, “Plankton is the base of the food web in all oceans”.

This made me feel a bit guilty. While we’re enjoying the beautiful Caribbean water due to the absence of plankton, the sea life must be struggling to survive without it! Well, not anymore. Over the years the sea creatures in this region have had to adapt and evolve in order to survive.

According to the Oceanic Research Group “The most successful solution to the problem [absence of plankton] is the coral reef community. The reef is a living structure made by coral animals. The reef itself is adapted to survive and grow in the tropical seas. As it grows, it provides a safe haven for fish and invertebrates to hide and make nests. This draws all kinds of life to the reef. The smaller fish draw larger fish and sharks. So the reef forms the basis of a complete ecosystem.”

I’m really digressing here but found it really fascinating. Coral Reefs … another topic for another day.

Back to the color of ocean water…

Why do we study ocean color anyway?

Much of the information I found was provided by NASA and oceanic researchers. It made me wonder why so much time, effort and money is put into researching the ocean’s colors. Certainly, it wasn’t to satisfy our need to know why the colors are so clear and blue!

Ocean color can be studied thanks to satellites that give us cool views like the one below. These satellites allow researchers to learn more than just ocean color. They also tell us about ocean bathymetry, sea surface temperature, ocean color, coral reefs, and sea and lake ice. 

Note the incredible water color around The Bahamas!

Combined with other forms of data collection, the colors of the ocean are studied for at least two key reasons.

Ocean Color is studied to Combat Red Tide

The National Oceanic and Atmospheric Administration (NOAA) studies ocean color to identify harmful red tides in the Gulf of Mexico. (Red tide is a phenomenon caused by algae blooms where there is so many they color the coastal waters brownish red).

The blooms may deplete oxygen in the waters and release toxins affecting sea life and people.

In fact, studying the ocean color and red tide, in particular, is helping the Florida Gulf Coast clean up its red tide problem. Who knew?

Ocean Color is studied to Monitor Plankton

The study of the ocean’s colors is also used to learn about the composition of plankton. Plankton makes up to half of the photosynthesis activity on earth providing over half of the oxygen to the earth’s atmosphere. I like to breathe, don’t you?

Consider that approximately 70% of the earth’s surface is covered by ocean, this means half of the photosynthesis in the world occurs in the ocean. It sounds like an important reason to study the ocean’s colors to me!

According to the National Academy of Science, monitoring helps assess the impact of concerns such as increased temp & ocean acidification, marine pollution, and overfishing.

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