Advanced 7 minutes
Navigating in low visibility
When you can't see anything, your reference stops being visual and becomes physical
In low visibility, the whole orientation system you've built collapses at once: there are no visual references, you can't see your buddy, you can't even tell the bottom from the ceiling if you get disoriented. What's left is what you can touch and what your instruments show.
In this article you'll see how navigation changes when visibility is poor, what references replace the visual ones, how buddy contact is maintained, and how the stress component is managed.
Low visibility isn't just uncomfortable: it's the condition where orientation degrades the most and where it's easiest to become separated from your buddy. It deserves its own technique, not improvisation.
Where poor visibility comes from
As you saw in the article on light underwater, visibility is determined by the scattering of light off suspended particles. The more particles, the more the light scatters, and the less contrast reaches your eyes.
There are several common causes, and it's worth distinguishing between them because they don't behave the same way. Suspended sediment, stirred up by surge, current, or by divers themselves, usually improves if you move away from the source. Runoff from land after rain affects wide areas and persists for days. Plankton blooms can reduce visibility drastically and tend to be seasonal.
There's a particular case worth recognizing: in some places visibility worsens drastically when crossing a halocline or a thermocline, as you saw in the article on temperature. There the murkiness is optical, not particulate, and it usually clears up by changing depth slightly.
And there's one source of poor visibility that you have complete control over: the one you generate yourself. Poorly oriented finning near the bottom can turn a dive with acceptable visibility into a blind dive for everyone coming behind you.
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