The Editor says: Divers have a love-hate relationship with currents. We all love diving when there's no current — but no current usually means no fish. Many overseas dive sites are famous for their powerful currents, so when you encounter a washing-machine current, upwelling, downwelling, or layered bi-directional current, how should you handle the dive safety risks involved? Many thanks to dive instructor 徐志綸 (Lancehsu) for his expert insights, which will help all of us stay calm and collected when we meet any kind of current underwater!
Dive Safety — What Types of Currents Are There?
After leaving Penghu, some instructor friends asked me about dive safety questions related to water currents. Here I'll turn what's in my head into words. Please don't take my articles as gospel — by the end it might all sound like nonsense, but take it as a reference and stay safe. How do we dive in current zones? How do we prevent problems and handle them when they arise? Currents can produce different flow patterns and speeds depending on topography and tidal range. Here we'll broadly categorize currents into five types:
- Unidirectional current (the most common and most straightforward — introduced in an earlier article about wolf packs and current speed at Penghu)
- Upwelling (rare)
- Downwelling (rare)
- Washing-machine current (extremely rare)
- Layered bi-directional current (rare — a dedicated article on Penghu's unique layered currents is coming)
When all of these occur together, we call it a chaotic current (extremely, extremely rare).
If you encounter chaotic currents exceeding 3 knots — (you're on your own and godspeed).
Today, let's use the dive site "East-West Ji Corridor" at the Southern Four Islands of Penghu as our example. First, an introduction to this site: "East-West Ji Corridor" refers to an isolated reef sitting between Dongji and Xiji Islands. The reef top is at 5 m and the base at 18 m. The channel formed between the two islands is, as the name implies, a waterway — and waterways are where currents converge. As the current accelerates through the channel and passes the isolated reef, it splits into branching flows. Additionally, the area surrounding the isolated reef is blanketed with large and small rock formations, each of which generates its own individual branching current. About 150 m south of the isolated reef, the depth is 20–25 m; as you approach the reef it gradually rises to 18 m, and about 150 m north of the reef it drops again from 18 m down to a 25–30 m wall.
Using the flood tide at East-West Ji Corridor as an example: during the flood tide, current flows from south to north. As it passes over the isolated reef, the topography shallows from depth, causing the current to converge and producing a short stretch of upwelling. Combined with the large boulders and low-lying terrain surrounding the reef, this generates S-shaped branching currents and downwellings. As you pass through this section of terrain, you'll experience what people call the washing-machine current, upwellings, and downwellings all at once. The converging currents cause acceleration, and current speed is typically 1 to 2 knots higher than the surface forecast. If the captain estimates 1 knot at the surface, the current around the isolated reef could be 2–3 knots — and so on.
Below, the Editor shares a strong-current experience encountered previously at Eluanbi, Kenting.
If You Encounter 3–4 Knots of Chaotic Current — What Should You Do Right Now? (You can also learn about current speed in this article)
First, stay close to your dive guide. Your dive guide may choose from the following options:
- Drift with the current (high risk of team separation): If you simply drift, you may miss the dive site entirely, and your dive buddies may scatter. If visibility is below 10 m, the likelihood is even higher.
- Hold position (wait for the current to ease before moving — though it's possible the current stays this strong for the entire dive): Tucking into a low-lying depression is absolutely the best way to shelter from current — it's very safe. You'll feel the water rushing intensely overhead; you can even hear it. The bubbles you exhale will swirl and sway all around you.
- Move hand-over-hand along the reef toward the dive site (less experienced team members may still get swept away): If you stop on top of a rock while moving, you'll feel the current shifting — one moment from the east, the next from the west. Bubbles will surround you, and when you turn to exhale, the bubbles will spiral away in a rotating pattern — the so-called washing-machine current. You may also encounter upwelling: it will feel as though, in addition to your hands gripping the rock, someone behind you is grabbing your scuba tank / cylinder and pulling you upward. (If you are inadvertently lifted, immediately switch to a head-down, feet-up position, vent your BCD, and kick against the current back to the bottom to shelter.)
- Abort the dive (surface immediately and end the dive).
There is no single best option — the dive guide must assess the situation in real time and consider the team's ability level to decide how to proceed.
If your team is highly experienced and you successfully fight your way through to the isolated reef with your dive guide, you'll be rewarded with an extraordinary sight: a massive school of fusiliers forming a spectacular waterfall against the current, while yellowtail snappers, soldierfish, and a host of rare and precious species shelter on the north face of the reef out of the current. The scene is truly breathtaking — even Lance, back from Palau, finds it awe-inspiring and utterly captivating.
Dive Safety — Currents
However, the moment you approach the top, eastern side, or western side of the isolated reef, you will encounter strong current. One thing to be especially mindful of at this dive site: when you begin your ascent for your safety stop, you will inevitably leave the isolated reef. Stay close to your dive guide — many divers become separated precisely because they let their guard down during the safety stop.
Safety Stops Are a Common Point of Separation
The instant you leave the isolated reef — whether toward the surface or in any other direction — the current will rapidly sweep you away. Visibility at this site is typically below 10 m, and depending on current speed, groups can easily become separated. At just 2 knots, roughly two minutes into the drift (approximately 120 m of drift from the reef), you may encounter a 30 m wall to the north of the isolated reef. At anything above 2 knots, this spot invariably produces an irresistible downwelling. If you're not paying attention, you could be dragged from 5 m down to 30 m within 30 seconds. In the two months Lance spent as a dive guide in Penghu, he experienced this type of downwelling twice at this spot — both times when current exceeded 2 knots, with one instance reaching 4 knots. If your remaining air is insufficient and a downwelling triggers panic together with critically low air, the risk rises sharply. This is why risk management at this site is stricter than at other sites, and why significantly more air must be reserved for the stop — and also why dive time is always shortened in strong current. During the safety stop, stay tightly together, hold onto each other, and hold onto the instructor.
Weighting in Current Zones
As a general rule when diving in current zones, divers with limited current experience are advised to add 1–2 kg more weight than usual, prioritizing comfort and balance underwater. This makes it easier to manage buoyancy if you encounter upwelling, and in an emergency, ditching your weights provides a faster increase in buoyancy.
What You Can Do Before the Dive
The five basic pre-dive safety checks: BWRAF
- B — Confirm your BCD inflates and deflates normally and has no damage.
- W — Check your weight system; it must be easily ditchable in an emergency.
- R — Check all five quick-release buckles, especially the scuba tank / cylinder strap.
- A — Confirm that both divers' air is turned on fully and the alternate air source (octopus / alternate second stage) works normally.
- F — Final check: fins, mask, surface marker buoy (SMB), and hose routing.
Correct pre-dive safety checks can prevent 80% of problems from occurring underwater.
Dive Safety Checklist for the Entire Dive
- Stay close to your dive guide: Keep track of the dive guide's position at all times, and always listen for the dive guide's bell or signal.
- Buddy system: Track your dive buddy's position. Remind your buddy to check air and monitor the dive guide's position and direction of travel. If you accidentally drift away, first signal the dive guide; if signaling is difficult, stay with your dive buddy. If a dive guide discovers two divers missing at once, at least both are together — which is far less worrying.
- Watch your bubbles: The direction your bubbles travel reveals the direction and intensity of the current.
- Air management: Check your remaining air far more frequently than usual. Reserve at least 80 bar for your safety stop, and inform your dive guide.
- Stay calm and relaxed: If you find yourself in a situation beyond your experience, don't panic. Focus on your depth, ear equalization, no-decompression time, and air management.
- Different currents in different terrain call for different responses. Here we'll share tips for one of the more dangerous scenarios: downwelling.
The following are Lance's personal experiences with downwellings in Orchid Island, Palau, and Penghu. Dive guides will typically brief you in advance about what currents to expect at a site and how to handle them.
- If it is a gentle, gradual downwelling, simply relax your body and gently equalize your ears. You may only descend 1–2 m; once you leave the current zone, resume your normal dive.
- If you are on a wall and the current is not too strong, you can climb hand-over-hand along the wall back to the reef top. If the current is too powerful to grip the wall, simply push away from it. You may descend 10 m or even deeper, but just equalize as you go — once you're clear of the wall, the downwelling will ease. Follow your dive guide and ascend slowly.
- If visibility is poor and you have no reference points, suspended in the water column, watch your dive computer depth. Switch to a head-up, feet-down orientation and swim toward the surface. If you are still descending, keep equalizing — you may need to partially inflate your BCD, keeping your hand on the inflate/deflate valve to control buoyancy continuously. Watch your dive computer depth closely; as you approach the surface, release air promptly to avoid a runaway ascent. During the ascent, your bubbles may surround you or drift slowly downward. You may not be able to see your buddy or instructor clearly; you may feel flustered — but don't over-panic. Control your buoyancy, slowly return to the surface, and if necessary, skip the safety stop entirely. That is perfectly acceptable.
- If during a downwelling you run out of air and cannot locate your instructor or buddy, perform an emergency ascent immediately: ditch all your weights, ascend to the surface, float on your back to maximize surface buoyancy, maintain proper fin kicks, and orally inflate your BCD to establish positive buoyancy.
What If You Lose Your Dive Guide, Get Separated from Your Buddy, or Accidentally Run Out of Air?
It's not always your fault. Maybe the instructor spotted something big and chased after it. Maybe your buddy got so absorbed in a creature that they drifted off. Maybe the current split your group apart. Maybe you panicked and took too-deep breaths. Maybe the instructor overestimated your ability. None of this is entirely your fault — so don't take all the blame on yourself. Deploy your surface marker buoy (SMB) and slowly return to the surface; everything else can be sorted out then.
Three steps when something goes wrong — stop, think, act:
Stop — stopping is what allows you to think calmly and solve the problem. As long as you still have air, you still have time to deal with whatever is happening underwater.
One-minute emergency procedure:
If you become separated from your buddy or dive guide, do a 360-degree rotation for one minute searching for them. If you cannot locate them, ascend to the surface rendezvous point. If possible, deploy your surface marker buoy (SMB) before surfacing.
One more note: Lance is 33 years old and has been teaching and guiding for 10 years. Across Taiwan's six major dive regions, Southeast Asia, Australia, the Maldives, and Palau, he has accumulated over 6,000 dives. He has dived in 4-knot current — but has never dived in a downwelling above 2 knots, an S-type current, or an upwelling without calling it inexperience in those conditions. Lance still has many places left to explore and continues to learn from every new experience.
So diving in a new environment always means being inexperienced there. Please respect your local dive guide, and respect local expertise. A dive guide is there to show you the underwater world — not to take you on a reckless adventure. We all want you to arrive with a smile and return home safely.
If there's no current at all, everything Lance said above is just hot air.
Wishing everyone eternal safe dives.
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