Glossary

Clear water lets you see 40m+. Poor visibility (less than 5m) happens when sediment, algae, or plankton fills the water. Lower visibility means you need better buddy control.

Wind far out at sea creates waves that travel long distances as swell. Bigger swells mean more water movement, which churns up sediment and reduces visibility underwater.

Strong winds create waves and chop on the surface. Different wind directions have different effects at each dive site depending on whether the site faces into or away from the wind.

Tides create water movement that can stir up sediment. Some dives are only safe at slack tide (when water movement is minimal) or at specific tide stages.

Light currents (under 0.5 knots) let you enjoy a gentle drift. Strong currents (2+ knots) require drift diving skills. Rip currents near shore can be deadly—never fight them, swim parallel.

The deeper you go, the more nitrogen your body absorbs. This limits how long you can stay down and requires safety decompression stops.

Imagine a sharp temperature drop at a certain depth. Above it's warm, below it's cold. You might feel this as you descend—it's like swimming through an invisible blanket.

Salt water is denser (heavier) than fresh water. The saltier the water, the more you float. A diver neutrally buoyant in the Caribbean might be heavy in the Dead Sea.

A high divability score means great conditions: calm winds, low swell, good visibility. Low scores mean rough water, poor visibility, or strong currents—consider diving elsewhere.

Some sites in clear tropical water can reach 50m+ visibility. Estuaries might only reach 10m at best due to constant sediment from rivers. Knowing potential helps plan what to expect.

Open Water (18m max), Advanced Open Water (40m), Rescue Diver, Divemaster, and specialty certifications like Nitrox or Wreck diving. Each builds on previous skills and knowledge.

Open Water allows you to dive safely to 18m with a buddy. Advanced and specialty certifications unlock deeper dives and technical skills.

You're either heavier than water (sink), lighter (float), or neutrally buoyant (stay put). Good divers master neutral buoyancy by adjusting their breathing and weights.

River water is lighter (less dense) than salt water, so it floats on top. After rain, estuaries get murky as river sediment floods in and reduces visibility significantly.

Turbidity is caused by sediment, algae, or plankton suspended in water. Rain stirs up sediment in rivers and estuaries. Storms churn up the ocean floor. Both reduce visibility.

Cold water holds more oxygen than warm water. Oxygen-poor zones (dead zones) occur where water is stagnant—these areas support little to no marine life and make diving unpleasant.

Cold, moving water holds more oxygen. Stagnant, warm water has less. More oxygen means more fish and healthier ecosystems. It's a sign of a thriving dive site.

Ocean acidification (lower pH) from carbon dioxide absorption stresses corals and shellfish. Most marine life thrives in a narrow pH range. Changes can damage entire ecosystems.

Reefs are underwater mountains or ridges made of rock or coral. They're home to thousands of species and create interesting diving with varied depths and features.

Below 30 meters, nitrogen becomes narcotic—it affects your brain like alcohol. You feel dizzy, confused, and giddy. It clears when you ascend. This is why deep diving requires special training.

The deeper and longer you dive, the more nitrogen your body absorbs. This accumulation limits bottom time and requires decompression stops on ascent to safely off-gas.

You must ascend slowly and pause at specific depths (typically 3-5 meters) so your body can safely release nitrogen. Skip this and you risk 'the bends'—a painful, dangerous condition.

As you go up, water pressure decreases and nitrogen comes out of your tissues as bubbles. If you ascend too fast, these bubbles form in joints and blood—painful and dangerous.

Wrecks are challenging dives because they can be dark, have strong currents, and have enclosed spaces. They're only for trained advanced divers.

Freshwater is lighter than salt water, so they don't mix instantly. Where they meet, you see a shimmering layer—it's like an invisible barrier underwater, pretty but disorienting.

Similar to a thermocline but related to overall density. You might ascend or descend unexpectedly as you cross it due to sudden density changes.

After rain, rivers dump sediment into the ocean. Storms and rough seas stir up sandy bottoms. More sediment = murky water = poor visibility for diving.

Bulky, loose gear creates drag like a parachute. Streamlining means tucking everything in tight and moving smoothly, so you use less air and tire less quickly.

Chlorophyll is what makes plants and algae green. It absorbs red light, so red colors disappear underwater before blue does. That's why everything looks greenish-blue at depth.

Imagine billions of tiny plants floating around. When conditions are right (nutrients + warm water), they multiply rapidly in 'blooms' that turn water milky or green and block sunlight.

These tiny creatures eat phytoplankton and are eaten by fish. More plankton means more food, which supports more marine life but might mean hazier water.

Water absorbs light. Red disappears first (around 5m), then orange, yellow, green, until only blue remains at depth. This is why deep wrecks look monochrome and gloomy.

Many creatures only come out at night. Night dives are magical and eerie, but require special training, lights, and good navigation skills.

Some creatures glow in the dark through chemical reactions in their bodies. Dinoflagellates create glowing water trails. It's otherworldly and one of diving's greatest rewards.

If you don't have enough oxygen in your bloodstream, you lose consciousness without warning. This is why breath-holding (freediving) is so risky and why breathing steadily matters.

Breathing pure oxygen (or oxygen-enriched air) at depth is toxic. Your body can only safely handle certain oxygen levels at certain depths—this is for advanced technical divers.

Unlike ocean swell that travels from far away, wind chop is generated right where you are. In shallow enclosed spots, the choppy surface reaches down and resuspends bottom sediment, clouding the water. The longer the fetch (open distance the wind blows over), the bigger the chop.

Even once the swell drops and the rain stops, the water stays murky for a while as particles slowly sink. How fast it clears depends on the seabed — rock and coral sites recover in a day or two, while mud and silt bottoms can stay hazy for the better part of a week.

A short period (under 8 seconds) usually means messy local wind chop. A long period (11+ seconds) is groundswell that has travelled from a distant storm — it carries far more energy, reaches deeper, and creates stronger surge even when the wave height looks modest.

A site tucked behind a headland might be glassy calm in a south swell but undiveable in an east swell. We compare the swell direction against each site's sheltered directions to work out how much wave energy actually reaches the water you're diving in.

Offshore winds (blowing from land out to sea) hold waves up and smooth the surface — ideal for diving. Onshore winds push chop toward shore and stir things up. Each site has an ideal wind direction based on which way it faces.

Wind needs room to build waves. A narrow sheltered cove has short fetch so it stays relatively calm, while a long open bay lets the same wind whip up significant chop that reaches down and clouds the water.

Wind rarely blows steadily — it comes in bursts. Strong gusts can quickly rough up a previously calm surface and make boat entries or shore exits trickier, even if the average wind speed looks manageable.

Despite the name, spring tides have nothing to do with the season. When the sun and moon pull together, high tides are higher and low tides are lower. The bigger water movement means faster currents and more stirred-up sediment — often reducing visibility.

Neap tides are the opposite of spring tides — the sun and moon work against each other, so the difference between high and low tide is small. Less water moves, currents are gentler, and sediment stays put, which often makes for clearer, easier diving.

Between the incoming and outgoing tide there's a short lull where the current stops. At sites with strong tidal flow, slack tide is the only safe and comfortable time to be in the water — plan your dive to hit it.

A large tidal range means a lot of water has to move in and out over a few hours, driving stronger currents. A small range means gentler flow. Knowing the range helps you anticipate how much current to expect.

SST tells you how much thermal protection you'll need and which species are likely to be around, and it shapes broader ocean conditions through the seasons.

Deep water is cold and packed with nutrients. When it rises to the surface, it fuels plankton blooms that feed everything up the food chain — great for spotting big animals, but the extra plankton can turn the water green and cut visibility.

Unlike the Divability Score (which is about surface safety), the Water Clarity Score focuses purely on how far you'll see. It distils the many factors that drive water clarity into a single easy number — higher is clearer.

Rather than reading charts, the briefing tells you in a sentence or two whether it's worth going, what the visibility and surface conditions are like, and what's driving them today. It's built from the same physics and forecast data as the scores.

Conditions don't recover the instant a storm passes — sediment stays suspended and runoff keeps flowing. The penalty keeps the score realistically low during this recovery window so you're not misled by a calm-looking forecast the day after rough weather.

Visibility is affected by many things at once, but usually one factor dominates. Identifying it helps you understand the conditions and predict how they'll change.

These often disagree, and that's the point. Big swell over a rocky reef can make the surface rough (low divability) while the water below stays crystal clear (high visibility). Always check both before deciding — one tells you if you can dive, the other tells you what you'll see.

If you surface too fast, dissolved nitrogen fizzes out of your tissues like a shaken soda, forming bubbles in joints, blood, and nerves. Symptoms range from joint pain to paralysis. It's prevented by ascending slowly and doing safety stops, and treated in a recompression chamber.

Almost every recreational dive ends with a safety stop. Hovering at 5m for a few minutes gives your body extra time to off-gas nitrogen gradually, dramatically lowering the risk of decompression sickness before you surface.

After a dive your body still holds extra nitrogen. The surface interval lets that dissipate. The longer you wait, the more nitrogen clears, and the more bottom time you get on the next dive. Diving again too soon raises decompression risk.

The deeper you go, the faster you absorb nitrogen, and the shorter your NDL. Stay within it and you can surface (with a safety stop) whenever you like. Exceed it and you must complete decompression stops or risk the bends — this is the line between recreational and technical diving.

During a breath-hold, oxygen drops. On ascent, falling pressure can cause it to crash suddenly, blacking you out just metres from safety — often without warning. This is why freedivers must never dive alone and always use a trained buddy watching closely.

As you go deeper, water pressure squeezes your eardrums. Pinching your nose and gently blowing (or swallowing) pushes air into your middle ear to balance it. Descend slowly and equalize early and often — never push through pain, which can rupture an eardrum.

Any air-filled space — ears, sinuses, lungs, even a mask — can be injured if pressure isn't equalized. The most serious is lung barotrauma from holding your breath on ascent. The golden rule of scuba: never hold your breath, keep breathing continuously.

Water pulls heat from your body far faster than air. Even in mild water, a long dive without adequate exposure protection can leave you shivering, clumsy, and confused. Proper wetsuit or drysuit thickness for the water temperature is essential.

Thickness (in millimetres) is matched to water temperature — a 3mm suit for warm tropical water, 5–7mm for cooler seas. The trapped water warms up and acts as insulation, so a well-fitting suit is far warmer than a loose one.

Unlike a wetsuit, a drysuit lets no water in. You wear warm layers underneath and add air to the suit for insulation and buoyancy control. This makes long dives in cold water comfortable, but requires extra training to manage the air properly.

The BCD holds your tank and lets you inflate or deflate to float, sink, or hover. Mastering small adjustments — combined with breath control — is the key to effortless neutral buoyancy and protecting the reef from accidental fin kicks.

The regulator delivers air only when you inhale, at exactly the right pressure for your depth. It includes your primary mouthpiece, a backup (octopus) for sharing air, and gauges. Regular servicing is critical since it's the piece of gear you literally can't dive without.

Rather than relying on printed dive tables, a dive computer constantly recalculates how much nitrogen you've absorbed based on your actual depth profile. It warns you before you approach limits, times your safety stop, and logs the dive automatically.

Less nitrogen means you absorb it more slowly, so you get longer no-decompression limits. The trade-off is that the extra oxygen becomes toxic beyond certain depths, so nitrox has a strict maximum depth and requires a short certification course.

When warm water meets abundant nutrients (often from runoff), microscopic algae multiply explosively. The water can turn pea-green or reddish and visibility plummets. Some blooms (red tides) release toxins harmful to marine life and humans.

Corals rely on symbiotic algae for colour and food. Prolonged warm water or pollution stresses the coral into expelling them, leaving bare white skeleton. Bleached coral isn't dead yet, but if the stress continues it will die — a major concern for reef divers.

Macro diving is about slowing down and hunting for the small stuff. It's ideal when visibility is limited, since you're only looking a few centimetres away, and it reveals a hidden world of bizarre, colourful critters most divers swim right past.

The unglamorous name says it all — the bottom looks like muck. But these sites are treasure troves of rare, weird critters like frogfish, blue-ringed octopus, and flamboyant cuttlefish. Good buoyancy is essential to avoid stirring up the fine sediment.

As you descend through a thermocline you often pass from warm clear surface water into cooler, hazier, plankton-rich water below — or occasionally the reverse. It's a natural boundary that can dramatically change both what you feel and what you see.

Divability is about whether it's a good time to be in the water — calm surface, manageable swell and wind, safe entry and exit. It's deliberately separate from the Water Clarity Score: a site can be perfectly safe to dive but murky, or crystal clear but too rough to get in. Always check both.

Great conditions don't line up often, and they can be easy to miss. When a favourite site or a region you follow is forecast to hit this top band, VisPro can send you an alert so you don't have to keep checking manually.

Unlike short, messy wind chop generated nearby, groundswell has organised into long, powerful lines. It reaches deeper and produces stronger underwater surge, so a modest-looking groundswell can stir up the bottom and rock you around more than a bigger, shorter local swell.

Onshore winds pile waves and chop onto the coast, stirring up shallow sediment and making entries and exits harder. Most shore dive sites are at their worst in a strong onshore wind.

Offshore winds groom the sea surface flat and clean, making for calmer, clearer, more comfortable diving. When a site's ideal wind direction is met, it's almost always an offshore or cross-offshore breeze.

Currents under about 0.5 knots feel like a gentle drift; 2+ knots demand real drift-diving skill. Wind is often quoted in knots too — roughly double it to get km/h.

Instead of fighting the flow, you go with it and cover a lot of ground with little effort. It requires good buoyancy, a surface marker buoy, and a boat or plan to pick you up downstream — never attempt one where you can't safely exit.

Heavy rain washes sediment and freshwater off the land and out through river mouths. This brown, nutrient-rich plume can smother nearby sites for days, which is why estuary and river-mouth dives are so sensitive to recent rainfall.

Deployed on ascent or throughout a drift, the SMB tells boat traffic exactly where you are and gives you a visible reference line. A must-have anywhere there's boat activity or current.

The 'octo' is a spare mouthpiece on a bright hose, ready to hand to a buddy who's low or out of air so you can ascend together. Checking it works is part of every pre-dive buddy check.

Achieved by balancing your weights against the air in your BCD and lungs. Good neutral buoyancy saves air, protects fragile reef from fin damage, and makes diving feel weightless and calm.

Partners confirm air is on, weights are secure with quick-release, the BCD inflates and deflates, and the alternate air source works. A quick habit that prevents the most common — and most avoidable — dive incidents.

Freediving is 'apnea diving'. Static apnea is holding your breath still; dynamic apnea is doing so while swimming. Proper technique and never practising alone are essential, because pushing apnea too far leads to shallow water blackout.

Pelagic species cruise the open blue rather than sticking to the reef. Sightings are less predictable but thrilling — often best in clear, current-fed water where nutrients draw them in close.

These tiny, jewel-like creatures are everywhere once you learn to look. Because you only need to see a few centimetres to enjoy them, nudibranch hunting turns a murky, low-visibility day into a rewarding macro dive.