What You Need to Know About Currents
From Scuba Diver Life
The thrill of flying over a reef, pushed onward by a strong current, can be one of the most exhilarating experiences in diving. But diving in currents can lead to problem situations if you’re not vigilant.
A number of factors cause currents, including the tides, wind, and thermally unstable water columns. Usually currents run horizontally, parallel to the earth’s surface — these are perfect for drift dives. Certain situations, however, cause currents to run vertically up (up currents) or down (down currents), while other currents can create a horizontal vortex. If a diver gets caught in one of these currents it can quickly lead to a dangerous situation.
A down current occurs when a current hits the face of a wall or when it runs at a right angle to a drop off. Down currents are also possible when two currents moving in opposite directions meet or move over each other. These types of currents have a nasty reputation among divers, and for good reason: they can quickly drag you far deeper than your planned depth. Sometimes this occurs gradually, and you won’t realize it until you feel the need to equalize, or until you look at your depth gauge or dive computer. But in some situations, a down current can pull you from 15 feet to 65 in a few seconds.
Most down currents lose strength the deeper they go, but don’t just wait for the ride to end, though, as there’s no telling how deep the current will take you. If you get caught in a down current, try to remain calm. Stop. Think. And then act. Maintain natural breathing to conserve air, and swim out into the blue. Although you may be in a scary situation, remember that down currents generally become weaker further away from the wall or drop off. While you’re swimming out, you also want to swim up — aim to swim a 45-degree angle.
If the current is especially strong you may want to inflate your BCD, but remember, an inflated BCD creates a larger surface area for the current to push against, so it might not help as much as you think. If you do inflate your BCD, prepare to deflate it rapidly once you’re out of the current to avoid a run-away ascent. Avoid dropping your weights unless you absolutely must.
Another option is to get as close to the wall as you can and climb up. The current is likely to be strongest here, and you might need to hold on to the coral to pull yourself up. If you must use this option, do so with caution and try to keep yourself and the coral as safe as possible. Try to hold on to dead coral and avoid stinging hydroids.
As with down currents, up currents can occur when a current hits the face of a wall. These are dangerous because they can pull you up to the surface very quickly, which can lead to a host of problems, including decompression sickness, a lung over-expansion injury or arterial gas embolism. Try to maintain the same calm as with a down current, and react similarly by swimming away from the wall or drop off into the blue. Deflate your BCD and swim down.
A washing-machine current occurs when the bottom typography bounces currents around. These types of currents can push you in all directions, creating a feeling of extreme disorientation, which can be amplified when your bubbles get swirled around, making it very difficult to tell which way is up. As with up and down currents, try to swim out of the current horizontally while swimming slightly against the push of the water to avoid drastic changes in your depth.
Very little information is available about vortex currents as they only occur at a few dive sites around the world. The best way to deal with this kind of current is to avoid getting caught in it all together. If you do get caught in one, try to conserve as much energy as you can, wait until you feel it weakening slightly and swim perpendicularly out of it. This video of Socorro shows how easily a diver can get caught in a vortex. Note the horizontal snake of bubbles that acts as an early warning that this kind of current is present.
How Do You Recognize Types of Currents?
You can often predict strong currents, horizontal or vertical, by looking at the surface of the water. Areas where the surface is choppy without a moderate to strong wind, mixed with areas of very smooth water, could indicate a strong current. If the boat that you’re diving from is tied to a mooring buoy, look at the direction in which the boat is turned. If the boat is tied off at the bow, the boat will be facing into the current; if the mooring line is tight, the current is likely moderate to strong.
Underwater you can tell which way the current is running by observing the sea life around you. Soft coral sways in the direction the current is traveling, and fish face into the current, so if you see a school of fish pointing in one direction, that’s where the current is coming from. If a school of smaller fish is swimming around freely in different directions, there’s probably only a slight current, if any at all.
Bubbles can also tell you a lot about the current. Strong down currents can sweep your bubbles into the depths, as can horizontal currents. One of the only ways to identify a vortex is by its distinctive, serpent-like horizontal river of swirling bubbles.
Current diving can be exhilarating and safe if you stay vigilant and practice good judgment. Learn to recognize different types of currents, and be prepared. If you’re diving in an area known to have currents, always carry a DSMB, or safety sausage, in case you get separated from your group and must surface alone. As with any dive, if you feel uncomfortable or find the currents too challenging, better to abort your dive and move to a site with more favorable conditions.