Underwater Visibility Measurement Methods
Candace Reno January 12th, 2025 Posted In: Articles Tags: SCUBA
SCUBA divers often chat a lot about the “viz”. The “viz” is the visibility underwater. Many divers on the same dive will tell you different answers when you ask them how the “viz” was. The underwater visibility measurement methods used are often not done on the casual dive so the visibility is anyone’s best guess.
However, you can pretty much enjoy a SCUBA dive anywhere that offers decent visibility. Often times, cold water lakes offer the best visibility, but some ocean locations can become quite remarkable in terms of how far you can see.
Underwater Visibility
What is underwater visibility? Visibility is how far you can see underwater—or, more simply, can you see clearly underwater in the conditions around you? Most divers will estimate during a dive how far they can see horizontally. As you can imagine, this is not accurate and can be different from diver to diver. It really isn’t all that important to know you’re visibility. Although, it is fun to brag about having over 100 feet of visibility!
Horizontal Versus Vertical Depth
Most divers will consider horizontal range as their visibility marker. These are estimates at best but the more you dive the more you will get better at guessing the horizontal visibility. Vertical visibility can be assessed when you are underwater but can be inaccurate.
If you are sitting in the bottom at 100 feet and can see the surface, then the viability is not just 100 feet, it could be a lot more! The visibility can also change based on depth as it may get darker as you descend.
Secchi Disk
The Secchi disk is one of the most accurate ways to measure underwater visibility. The disk is attached to a line and gradually moved until the person holding the end of the line can no longer see it from the surface. This is great for measuring vertical depth. Factors that can affect the ability to see the disk are water color, chlorophyll, and suspended particles in the water column.
The deepest a Secchi disk has ever been recorded was about 262 feet (80 meters) on October 13, 1986 in the Weddell Sea near Antarctica. This is the theoretical maximum depth that the Secchi disk can be visible in absolutely pure water.

Other Methods For Measuring Underwater Visibility
To measure the underwater visibility, scientists can use photometers. More recently, satellites have also been developed to measure underwater visibility. You can look up the satellite data from around the globe and see the visibility at various locations!
What Affects Underwater Visibility?
Current
Current can be present or absent on a dive and can change in speed. Heavier current will pull up more silt from anything on the bottom or surface and take it with it. It’s important to make sure you are close to your buddy with current and especially reduced visibility.
Weather
The weather can affect the waves and water movement which in turn can affect the amount of particles in the water.
Bottom Contour
SCUBA dive sites that have a sandy versus rocky or reef bottom are going to have more problems with visibility just due to the fact that the sand can easily be picked up into the water column by divers, animals, or current.
Thermoclines
In normal thermoclines, there can be a layer of water that is more turbid than the rest of the water. When you are in it, visibility is significantly reduced, leaving you wondering: can you see clearly underwater at all? I’ve seen currents come in and cause thermoclines where it is very difficult to see underwater. I would describe it as fuzzy.
One particular time I was in St. Lucia and kept scrubbing the outside of my mask while on the dive to try and get the mask clear because it felt like it was fogging up on the outside.
Other divers
Let’s face it, no one likes to SCUBA dive in a big group of inexperienced divers. However, it can happen. Some divers are unaware of the environment or still fine tuning their buoyancy skills and kick up silt reducing visibility. The worst possible times are when you are down close to the bottom trying to take a picture of the nurse sharks sleeping under the ledge. Or even worse: when you are in a swim through and the person in front of you kicks up everything making you go into a blackout situation. Yes, these are situations I have personally encountered.
How Much Does Underwater Visibility Really Matter?
In the end, SCUBA divers are going to mostly estimate underwater visibility and not bother with an accurate measure. Dive operations or other ocean personnel might have the need for accuracy for their own reasons such as scientists tracking light availability for plant growth. Ultimately, we all strive to go diving in visibility that is over 100 feet! Beyond that, does it really matter what it is?
If it’s less than 40 feet, divers will be less excited about diving. However, in some areas, 40 feet is considered excellent for the location. Thus, great visibility good enough for diving can be hard to measure. Also, what seems like great visibility for one diver might be poor for another. For me, as long as I can see further than my hand underwater, I am good to go diving!