Murky Waters

Visibility underwater can be deteriorated by several factors including, run-off water after heavy rain, sediments stirred up by waves or currents, planktonic blooms. Moreover, it is often the action of the divers that can disturb the sediments, compromising the visibility. It is therefore important to correctly assess the risks connected to diving in reduced or zero visibility.

Several factors affect visibility in the water, which, in extreme situations, can be reduced to zero. Muddy bottoms can be easily disturbed by divers, creating clouds of sediment. In caves and wrecks, the movement of water due to the rise of bubbles can also cause a sudden reduction in visibility due to the detachment of the finer particles of sediments that often cover the walls of these environments.

Diving in very low or no visibility is challenging and stressful, exposing divers to risks such as getting trapped or losing their bearings. Turbid water can also indicate the presence of biological and chemical pollutants, with further problems to be addressed.

Learning to plan and manage dives in low-visibility conditions takes time, knowledge, and experience. The setup of the diving equipment should be specific with a “clean” profile, reducing the risk of getting caught. Even the psychological aspect is not to be underestimated; moving without being able to see is often a cause of stress that, if not controlled, could degenerate into panic.

The senses that generally contribute to our orientation are:

  • Sight: The eyes provide information about our position and surroundings by contributing up to 90% of the sense of direction.
  • Vestibular system: The inner ear senses acceleration in three dimensions.
  • Somatosensory system: it consists of a series of nerves that feel the gravitational field and provide additional information about our position, for example, whether we are sitting or standing.

During the dive, both the vestibular and somatosensory systems have reduced sensitivity, and therefore, our sense of orientation is based, in fact, only on sight. If visibility is reduced, it is very easy to become disoriented.

A disorienting effect has been observed by helicopter pilots when the rotor’s airflow kicks up a cloud of dust surrounding the aircraft. Its underwater counterpart is represented by clouds of plankton or sediments carried by the current that can determine a sensation of movement contrary to the real one. In extreme cases, you can be so confused that you cannot understand the up or down direction with obvious potential severe consequences.

A specific set of risks is associated with diving in reduced visibility, and appropriate mitigation strategies must be applied.

  • Entanglement: Getting caught in structures such as cables and nets is easier in murky water. To mitigate this risk, the diver should move cautiously, keep the equipment as close as possible to the body by securing the regulator around the neck with a special elastic tie, and have adequate cutting systems well positioned. It’s good to have a cutter for monofilaments, scissors for cutting thin cables, and a good knife for thicker ropes. These systems should also be positioned in easily accessible parts such as the forearm and chest. The “classic” knife position along the calf can be challenging to reach by a severely tangled diver, and the knife itself could become a potential tangling point.
  • Communication: in conditions of reduced visibility, the traditional communication system with hand signals is of limited or no use. In these cases, divers may consider using a connecting rope with an associated code of signals to communicate predetermined information. For example, one shot to draw attention, two to signal that everything is okay, etc. The amount of information that can be transmitted with this system is limited. For more complex communications, it is necessary to use acoustic systems that allow divers to talk to each other and, possibly, to the surface.
  • Safety procedures: Divers must be able to operate their equipment and that of their buddy by touch. In particular, open and close the cylinder valves, remove the ballast system, and use the BCD controls. The procedure in the event of separation from the dive buddy must also be reviewed, considering that you are in zero visibility conditions.  In this case, any attempt to find the other diver underwater is futile; it is better to go up in a controlled way, possibly deploying an SMB, and reunite once on the surface.

As in many other situations, safely handling dives with reduced visibility takes time and practice. A variety of exercises can be used during training in a controlled environment. A very good way to become familiar with situations of zero visibility is to use a blind mask, for example, by covering the glass with black tape while working on your equipment, identifying objects, or following a predetermined route. To ensure their safety, the diver in training must be accompanied by a support diver ready to intervene in case of need.    In any case, diving in significantly reduced visibility is not for everyone; if a diver feels discomfort diving in such conditions, in no way should they feel obliged to do so because, in an actual emergency, their behavior could become unpredictable, jeopardizing their safety and that of the other divers.