Visibility Underwater – what makes it good or bad?

Davy Jones Lockerinstructor Dani has written a new article for the DJL Blog. She explains what the different factors are that can affect visibility underwater. Even on a tropical island such as Koh Tao visibility can vary, however this doesn’t prevent divers  from seeing a great deal of coral and marine life once they are underwater.

visibility underwater what makes it good or bad ?

“What affects visibility underwater?

So this month has seen significant ups and downs in our underwater visibility on the island. There are still amazing dives but in both great and poor visibility.

Here is a list of the main things that affect visibility under water.

• Suspended particles

Sediment particles become suspended when water movement or divers disturb them. There are a number of natural causes of water movement that force particles into suspension. These include currents, the action of the waves, rough seas, runoff, and bad weather. A diver can stir up bottom sediments and reduce visibility in a variety of ways. For instance, by not using the correct kicking technique and using their hands to swim, or by landing on the bottom. Reduced visibility underwater is one of the many reasons that these actions are discouraged.

• Haloclines

Water of different salinities forms distinct layers. The interface between the two layers is called a “halocline” (halo = salt, cline = gradient). There are a variety of areas where haloclines can be found. For example in estuaries, or at springs which come to an end at the ocean. Other areas where haloclines occur include inland caves and caverns. The effect of mixing fresh and salt water may also cause a blurry effect which can be seen near the surface of the ocean. For instance during a rainstorm over the ocean. We don’t come across haloclines here in Koh Tao. It is still very interesting to research though. You may find fascinating videos with haloclines in Mexican cenotes.

• Thermoclines

The term “thermocline” signifies a temperature gradient (thermo = temperature and cline = gradient). The term can also describe a level at which water of two different temperatures meets. Water of different temperatures layers in a similar way to water of different salinities. However the effect is not as pronounced.

• Organic Particles

Algal blooms can disturb the visibility in a very dramatic way.  This sort of visual disturbance is often found in bodies of fresh water which have little or no circulation. Algae and bacteria are sensitive and the temperature, salinity and light conditions they require is very specific. They may be present only seasonally.

So there we have it then. The many different reasons as to why visibility can be great, or in some cases not so great. We can still have great dives in both conditions however. If you are training in poor visibility it can even be a bonus as it will create further ‘limits’ for future dives.

Happy diving guys 🙂 ”


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