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How to predict good visibility?

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Active Member
Jun 16, 2020
What are some of the key indicators you look for to assess whether the visibility is likely to be good or not?

I went out yesterday evening and was predicting poor visibility as it had been the 2 days prior but it was really good. Would love to know what to look out for in terms of wind direction, speed, swells etc
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My 2 cents: No rain for several days previously, as rain washes debris into the sea. Wind from the sea towards the shore of interest tends to stir things up, bad sign especially if the wind is moderate to strong. l associatr no wind or light wind from land concerned towards the sea with clearler conditions, especially if the wind is light. The above apply on dive day, and sometimes a day or two or three or four beforehand too.

The GB Windmap website can be useful. Click on the wind arrow nearest to your intended dive site.

I don't know if it's valid or sometimes valid but I often take sea surface chop as a bad sign. Not least because it often leads to sea sickness :sick: A flat mill pond like surface is usually a very good sign in my experience.
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What are some of the key indicators you look for to assess whether the visibility is likely to be good or not?

I went out yesterday evening and was predicting poor visibility as it had been the 2 days prior but it was really good. Would love to know what to look out for in terms of wind direction, speed, swells etc

If it were very high seas with churned up bottom, it will take a day or two for the visibility to improve even if the sea is flat the day following the storm. This depends on the locations and prevailing water conditions. Generally, it is guess work that has a high probability of error and can't beat showing up at the site and checking visibility with your own eyes. To do it accurately means that you have to predict wind direction, speed, currents, tides, rain vs. sunshine, sea bottom topography, depth of dive site, bottom composition (sand vs. rock vs. plant life, etc.) and God knows what other local factors that all have to line up perfectly in the prediction of each one of them to make a gross prediction that includes all of the factors to predict again the visibility. If any single factor deviates from its predicted state, the sum of the predictions will fail making the visibility prediction wrong. At the end, you have to show up at the site you intend to dive and observe the visibility with your own eyes and decide if it is worth diving.

My opinion above is shaped by my several decades of primarily shore diving in the southern Mediterranean, NE USA (New England, NY and NJ) and other locations around the world.
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Good point about location. Some locations are "fussier" than others. Perhaps due to the type of bottom (sand, rock, weed, etc.) and sheltering factors, such as reefs, sand bars, headlands, spits, harbour walls, tombolo, etc.
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Bottom conditions - silt/mud takes longer to settle than coarse sand. Also, a lot of other divers in area can stir up a mess.
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What are some of the key indicators you look for to assess whether the visibility is likely to be good or not?

I went out yesterday evening and was predicting poor visibility as it had been the 2 days prior but it was really good. Would love to know what to look out for in terms of wind direction, speed, swells etc
Ha ha if you figure this one out, let me know! Some places viz is correlated with the tide - better as the tide builds than as it recedes, but that won't work everywhere. River mouths or surface runoff is another obvious problem. Some places it's clearly affected by swell height stirring up stuff in the shallows. Around here in northern California, where the problem is mostly plankton I believe, there's no predicting it, aside from winter being generally better than summer.
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As said by other posters, Rain will make water muddy for several days
i remember one time i had only a week on the coast, and it rained the 1st day, it took 3-4days for water to start to clear up
also, if its close to an estuary, it's gonna be bad after a rain
gulfs and the like will stay bad longer than caps, caps usually clean fast because of sea currents
swells also count, specially when its sandy shore (in case you're doing shore entries)
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Income tide usually leads to good visibility. But there's not exact science when spearfishing.
While great viz is calming and beautiful - medium or slightly bad viz can certainly yield fish. I think since you can hide more, fish need to get closer to you to check you out:)
But yes, rising tide, no rain and an offshore wind rather than onshore can all help.

Sent from my iPhone using Tapatalk
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I'd agree with everything above as confounding factors. And probably more.

Once I get eyes on the beach I'm looking at particular patches of kelp where I know the depth to see how far down the stalks I can see with binoculars. Say one patch in 10 feet of water. Another in 20'. Sometimes it's tricky. But it helps.

At least then I know a little bit about what to expect and maybe how far out I have to swim to even have a hope of better vis. It's always a treat to find that it is muddy up top and clearer at the bottom.

And in all seriousness, no matter what the vis, if I get to the shore I'm diving most trips, unless conditions are dangerous, like high surf. I just think that's what it takes to fish in California. I'd spend too many days at the coffee shop grousing about bad vis if I didn't.
Also direction currents in the open water.Land wind on the coast versus sea wind, Sea to the land wind brings a indesisive yes or a no to goto fish,.Me and my spear fishing friends discuss probability of the water condition,Then we communicate by phone with the forever eager and hopefull o.a.p whom fishes from a stone walk way peir inturn we receive the wisdom from a near Merlin man figure describing from abouve the surface how many meters of depth if he sees the bottom or 2 3 meters we go to fish,Then there is a day when after 3 4 meters the water becomes clear or with variation visibility layers with fish showing them selfs on times
Thought I'd chime in since I've been dealing with bad visibility lately. For where I'm at in Hawaii, all of the above mentioned possible causes are valid. Wind, swells, tides/current, bottom conditions, weather. Mostly rainfall runoff and whether the area has sandy, silty, or dirty bottoms. I also take a look at what kind of soil is on land where the water is running off from. There are some places where it's mostly lava rock on land, so visibility is better after a rainfall event than areas where fine soil exists on land. Usually visibility from rainfall runoff clears up in a couple days, but in some areas it takes weeks. So it all depends on the physical nature of the area.

Other than runoff, swells have a big impact on visibility, depending on what's on the bottom. Normally anything above 5ft swells with sandy bottom is asking for poor vis.

Current usually runs along the coast, so visibility after a rainfall can almost instantly clear up if you pass the mud cloud or if the current changes direction. However, this is usually temporary as you'll soon run into another poor vis area. Hard to escape runoff.

I've seen wind blow huge amounts of soil into the coastal waters when the wind is high and especially after a fire, since there's no vegetation holding the soil together. I haven't found chop from the wind to be too much of a contribution towards poor visibility.
I mostly dive in large cold lakes that have a bit of wind activity from here to there and expect poor visibility due to the wind but not from runoff or dirt as the shoreline is all crushed or solid rock. Visibility is worse the further from shore I get, with a lake that is 700' deep 1/4 mile off shore I would expect much clearer water. Is the algae on the rocks the biggest culprit? A similar nearby lake with significantly more sand is much clearer. Another close alpine lake at about 6000' has pretty much a mud bottom at 40-50' with a bit of grass/moss but is always impeccably clear but never above 60 DegF. I don't see a great correlation or predictability, except in the spring when pollen fills the lake.
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