When we travel across the islands of the Andaman Sea, the first thing that captures our eyes is the color of the sea. Some places shine crystal blue, others glow emerald green, while in certain seasons the water turns cloudy with suspended sediments. These colors are not just stunning backdrops for photos—they are natural signals that reveal the quality of the water and the balance of the ecosystem.
Table of Contents
The Science Behind Sea Colors
Light Absorption and Reflection
Water molecules absorb red, yellow, and green wavelengths of light while reflecting blue. That is why most seas appear blue. The clearer and deeper the water, the more intense the blue becomes.
Phytoplankton and Organic Matter
When large amounts of phytoplankton or microalgae are present, the water reflects green. This often means the sea is rich in nutrients that support marine life.
Sediment and Pollution
Dust, soil, and sediments carried from rivers or rainfall can turn the sea brown or murky, usually indicating reduced water quality.
Shades of the Sea and Their Meanings
Deep Blue
- Science: Found in deep, clear waters where most wavelengths are absorbed, leaving only deep blue reflections.
- Water quality: Very clean, low in sediments and plankton, but also lower in nutrients.
- Ecosystem: Not rich in small creatures but often home to larger animals such as tuna, whales, and manta rays.
- Tourism: Not ideal for coral diving but perfect for liveaboard expeditions and luxury yacht cruising.
Crystal Blue
- Science: Extremely clear water with low turbidity; underwater visibility often exceeds 20–30 meters.
- Water quality: Pristine, usually within marine protected areas.
- Ecosystem: Supports thriving coral reefs and species like parrotfish, green sea turtles, and sailfin tangs.
- Examples: Similan Islands, Surin Islands.
- Tourism: World-class diving destinations attracting travelers globally.
Emerald Green
- Science: Caused by reflection of light through moderate levels of phytoplankton and algae.
- Water quality: Nutrient-rich and productive for marine life.
- Ecosystem: Supports schools of small fish, prey for larger species like mackerel and barracuda.
- Examples: Maya Bay (Phi Phi Islands), Maiton Island.
- Tourism: Popular among photographers; aerial drone shots are particularly breathtaking.
Dark Green
- Science: Indicates high plankton density, often signaling excess nutrients.
- Water quality: Can lead to plankton bloom and reduced oxygen levels.
- Ecosystem: Risk of red tide events where marine life suffocates.
- Examples: Some bays of Phang Nga during monsoon season.
- Tourism: Not suitable for snorkeling but scenic for boat tours.
Milky White
- Science: Suspended sediments from river runoff, storms, or heavy wave action.
- Water quality: Not always poor, but turbidity reduces light penetration.
- Ecosystem: Can stress corals that depend on sunlight for photosynthesis.
- Examples: Post-monsoon waters in Phuket or Krabi.
- Tourism: Better for beach walks and sightseeing, not diving.
Brown / Murky
- Science: Indicates pollution or heavy sediment, often from human activities such as sewage or harbor runoff.
- Water quality: Degraded, long-term exposure may cause ecosystem collapse.
- Ecosystem: Coral reefs suffocate under silt, and fish migrate away.
- Examples: Near river mouths in Takua Pa or busy harbors in Phuket.
- Tourism: Unsafe for swimming; best avoided for health reasons.
Golden / Reddish Tint
- Science: Sometimes caused by special plankton reflecting golden-red hues, or by sunlight at dusk.
- Water quality: If due to sunset, harmless; if due to plankton bloom, it may be toxic.
- Ecosystem: Red tides can kill large numbers of marine species due to oxygen depletion.
- Examples: Occasionally in enclosed bays with low water exchange.
- Tourism: Can be stunning at sunset for photography, but harmful when linked to plankton bloom.
Examples in the Andaman Sea
- Similan Islands – Crystal blue waters with colorful coral reefs, parrotfish, and soft corals.
- Surin Islands – Clear green-tinted waters near Moken Village, rich in plankton and small fish.
- Maya Bay, Phi Phi Islands – Emerald green waters created by sediments mixing with plankton.
- Phang Nga Bay – Often cloudy due to river inflows carrying sediments.
What Sea Colors Mean for Travelers
- Clear blue: Best for snorkeling and diving.
- Emerald green: Great for spotting marine wildlife such as dolphins and capturing aerial photos.
- Cloudy or brown: Poor visibility, unsafe for diving or swimming.
How to Keep the Sea Crystal Clear
Final Thoughts
The color of the sea is more than just a beautiful sight—it is nature’s language describing the quality of water and the health of marine ecosystems. By learning to read these colors, we can better appreciate the Andaman Sea and feel inspired to help protect its clarity for generations to come.
Want to see these shades with your own eyes? Book a trip with Phi Phi + Bamboo Island Tour or Surin Islands Tour and discover how each color tells a unique story of the sea.