Often, the difference between a great dive and one that felt almost like a complete waste of time is a matter of something as mundane as a measurement. When visibility is great, even the most boring site seems somehow magical; when visibility is poor, even the best reef or wreck seems dull. Here is a quick tutorial designed to help you learn how to determine which sites offer the best visibility.
Three Factors Affecting Visibility
There are three main factors that affect visibility underwater; often, they are directly related to one another. These factors are: suspended particulate matter, biological species or lack thereof, and light penetration.
Sunlight plays an incredibly important role in our ability to see what is around us. When the sun is shining, visibility tends to be better than on cloudy days, and when the sun is overhead, visibility is better than it is when the sun is at an angle. In addition, when the surface is glassy, it allows sunlight to penetrate better.
Biological species that affect visibility include plankton and algae, both of which bloom steadily during the spring in seasonal waters such as those around the coasts of North America. During a plankton bloom, when these tiny organisms are taking advantage of warm upper water layers for fast growth, visibility tends to improve once you get into deeper water where the sun’s light doesn’t penetrate as well; this is due to the lack of tiny organisms, not due to increased light penetration.
In areas where coral, sponges, and other filter feeders are healthy and active, they play a major role in clarifying water, which is why the Mediterranean and Caribbean regions tend to offer such great visibility.
Particulate matter, such as sand or silt, affects underwater visibility in the same way as a cloud of dust affects visibility in the desert. These tiny particles absorb part of the light waves that penetrate the water, and scatter much of the remaining light rays, so that by the time the remaining light hits our retinas, there is not much to see at all. Both water movement and the size of particles, as well as the weight of those particles, affects the way in which they in turn affect visibility. Heavy sand particles don’t float nearly as well as lightweight silt does, and very coarse matter, including gravel and pebbles, barely move at all unless conditions are severe. After a storm, choose a site with heavy bottom substrate and you’ll enjoy better visibility than at sites where particulate is lightweight. Tidal movement affects visibility, too; when you dive near shore, do so at slack tide or high tide for best visibility. Last, but not least, remember that runoff after rain can greatly affect visibility. Waiting a few days for water to clear is the best course of action you can take.
Diving during winter, when algae and plankton blooms are less likely, or heading to lower latitudes where the sun’s light penetrates year-round are two excellent strategies for enjoying great visibility. Paying close attention to tides, and diving when the weather is calm are two additional strategies you can use. With just a little attention to detail and some careful planning, you’ll enjoy the best possible visibility any dive site has to offer.