Every scuba diver enjoys taking the scuba gear package in waters that are crystal clear. They offer the best chance to enjoy the beautiful underwater marine life and topography. In some waters, however, the visibility is not so great. Other times the water could be murky with zero water visibility.
But what exactly is visibility? It refers to how clear the water is and is measured horizontally.
Underwater visibility is how far you can see when under the water. it can also be referred to as viz and you may have come across something like 50 feet of viz. This simply means that you can see up to a distance of 50 feet.
These are the main factors that affect visibility underwater
1. Water particles
Water particles are the main culprit behind low water visibility. These occur when the bottom of the river, sea, or ocean is stirred up by waves or currents and sometimes even by the diver with poor swimming and kicking techniques.
It’s important to have the best scuba fins while diving.
The type of sediment or particles at the bottom will determine the visibility level. Sand for example will make distant objects appear blurry. However, left to settle, the particles easily go to the bottom. On the other hand, in a river where there is clay at the bottom, it will get stir easily and can reduce the visibility to zero.
Clay also doesn’t settle to the bottom easily and will take a long time for the sediments to settle.
2. Haloclines or salinity gradients
Salinity gradients refer to the different levels of salinity in the ocean or seawater. The deeper you get the more saline the water becomes. When the water is calm, the top layers can be quite clear and if you were to stare down onto the haloclines, you would notice that the lower levels appear like an underwater river.
But what happens when the haloclines are disturbed? Visibility quickly reduces. While light can penetrate, there will be no clarity. Think of swimming in Vaseline. In this case, divers may even have a hard time reading the dive computer.
You will find haloclines at estuaries or at the springs that are about to join into the ocean or sea. You will also often find them at caverns or inland caves. Another way to see what happens when freshwater mixes with seawater are the blurry effect that occurs during the rains.
To prevent loss of underwater visibility brought about by a halocline, divers will need to swim at below or above the depth of different haloclines. Once the diver swims away from the region where different salinities mix, the visibility gets better and the water becomes clearer.
3. Thermoclines or temperature gradients
Thermoclines refer to changes in temperature levels of the water. This is where types of water with different temperatures mix. The effect is similar to a halocline. However, it is not as pronounced.
The colder the water the denser it is and will therefore sink under the warm water. The temperature of the water will thus drop as you dive deeper.
When there is a major difference between the temperature of water at different levels, the water appears oily which is very similar to a halocline. And as the diver rises through the different levels of water, he will observe quite a wonderful visual effect as the temperatures and thus clarity changes.
A good scuba mask will enable you to view the different thermoclines as you make the ascent.
4. Organic particles in the water
Yet another major factor that could affect the water visibility of the water is algae blooms and bacteria. One of the most likely spots for algae to bloom is in freshwater where the water is calm. Often for algae and bacteria to thrive, the salinity, temperature, and condition of the water need to be very specific. This often only happens during certain seasons.
For example, at Mexico Canote carwash, an algae bloom will happen during certain times of the year. This results in a greenish cloud that starts at around 5 feet to the surface. To reach the waters of the Canote which actually crystal clear, divers will need to get through the opaque layer formed by the algae.
To make sure you are always aware of the direction, always have a dive compass.
5. Hydrogen sulfide
You are not likely to come across hydrogen sulfide unless you are doing a bit of cave or cavern divining. Check out the beginner’s guide to cave diving. Often hydrogen sulfide will occur in freshwater that is not circulating. Also, there will often be a decaying organic matter.
In Cenote Angelita in Mexico, you can find waters with large qualities of hydrogen sulfide which turns the water foggy. Sometimes it may appear as smoke-like wisps.
If you were to dive in water that has a high amount of hydrogen sulfide, the visibility would be almost equal to zero. The visuals effects however are an absolute fascination.
6. The light
It is not hard to see that the sunlight and level of penetration will have a significant effect on the level of visibility. As you can see better and further during sunny days, the same principle applies when you get into the water.
Three main things will determine just how much light penetrates. One is the light conditions of the day and whether the day is cloudy or a bright cloudless day. Of course, you cannot influence the clouds but it is possible to perform planned dives on days when there is optimal light penetration.
Keep in mind that if you are diving close to the equator, there is a lot more sun which is can penetrate deeper into the water. These waters are perfect for bringing along your diving camera.
On the other hand, if you are at higher altitudes there is a lower angle of incidence which causes the majority of the light to be reflected. This is the reason why the waters are clearer in more tropical temperatures.
Another thing that affects the penetration of light is how the sun is located in the sky. You are going to have more light penetration at midday than at any other time of day. The angle of incidence reduces as the sun sets which also causes lower water visibility.
The third factor that affects light penetration is the state of the sea. Light is reflected more in rough seas than in calmer seas. This means that if you’re able to choose between dive sites, you should pick one that has calmer waters.
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The clearer the water the better it is for diving. Being visual creatures, we want to see better when we are under the surface of the sea. By understanding the different factors that affect underwater visibility you can pick the best dive spot and the right conditions to take the plunge.
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- How suspended particles affect visibility, scubadivingtheory.com