"We had a 3 knot current and were swept along the reef for at least two kilometers!" If I hear that I conclude, that it was either a very short dive (3 knots = 5.4 km per hour, so you make 2 km in 22 min.) or the current couldn't have been much more than a knot (2 km per hour is 1.1 knot).
The strength of current is measured in knots. A "knot" is a nautical term for the velocity of a nautical mile (6'076.1 feet = 1.852 km) per hour. The same for divers who talk about going with 60km per hour over a reef - that would actually be a 32 knots-current!! Sure feels fast, when you do a drift dive, but belive me, anything over 3 knots is very strong! Even a 3 knot current could transports you over 5 kilometer during a one hour dive (3 times 1.8 km = 5.4 km - since the current is pushing you, you are actually slower) - makes you glad if the boat crew is attentive and following you on surface to pick you up!
It is difficult to judge currents, but there are some indicators, which will tell a good observer more or less the rate of current. Fish react according to how strong the current is. Some seek shelter, others thrive in strong current. Observe small schooling fish like anthias or basslets and watch bigger fish like mackerels or trigger fish.
The small fish are swimming in every direction, in large schools distributed both vertically and horizontally over the reef.
Anthias and damselfishes in no current
Light current (to 1 knot):
The small fish are aligned, all facing up-current. If they are still in large, spread out schools, the current is around a half-knot. lf the schools are low and wide, swimming close to the coral, the current is closer to one knot. You are able to fin against this kind of current for a short time.
Medium current (1 to 2 knots):
The small fish are now hovering in a school spread out just barely above the coral and finning madly. A current of this strength begins to show in the behavior of the larger fish as well. They face the current and tend to concentrate behind coral heads or in other lee areas (lee =away from the wind / current). Most fish will now swim against the current, so if you do a drift dive, schools of fish will come towards you. In this kind of current it is already difficult to swim against.
Strong current (2 to 3 knots):
In this kind of strong current, the small fish are not seen, because they are all hiding among the branches of the coral. The big fish are gathered in lee areas, or very close to the bottom. On a drift dive in this kind of current you won't be able to stop and fin against if you want to look at something close up - so just enjoy the ride!
Very strong current (3 knots):
Now you won't need the fish as an indicator anymore. You are either swept along on a very fast drift dive or hiding behind a coral head. If you move your head around and face the current full on, your mask is fluttering and threatening to fly off, and your regulator begins to free-flow.
Too strong current
My opinion is that anything over 3 knots is so strong it is dangerous for a diver!
Down current (vertical current down):
This is an area with fast downward shifting water which is coming from the surface. There are two indicators for this type of current. Fish are not swimming horizontally but vertically, mostly down but also wildly up and in circles. At the same time your bubbles start to go down instead up until the air is sucked down as soon as it leaves your mouth.
When large fish like mackerels are swept down past you, while clearly trying to swim up again it is time to find a coral head or a overhang to press closely against or hide under. Because if not, as soon as the current reaches more than a knot you won't be able to fin up against it and inflating your jacket won't help you either!
Down current - this photo was shot under difficult circumstances!
Sometimes you have to do, what I call "Geko-diving" (geko = lizard) - climbing the coral wall, pulling yourself up with your hands and finning.
I know, this is very bad for the corals, but believe me, if the alternative is being swept down to 40 plus meter you do it! Try to only hold on to dead coral heads or other areas without life! Watch out for stinging hydroids.
The difficult part is not yet over, you still have to surface. I strongly believe it is better to try finning up than inflating your jacket, if you have to go against a down current. Actually in this kind of situation inflating the jacket is very dangerous, because if the down-current eases just a bit you shoot up to the surface like a cork!
I try to surface over the reef top and not out in the blue so
in case the current shifts or gets stronger I am only swept down to the reef.
Sometimes though it is better to get away from the reef because the current
is weaker there. Sometimes you face some hard choices.....
Read about my "worst dive ever".
We waited for 10 min in a strong down current before we decided to do geko-diving
Up current (vertical
You don't know how bad currents can be, until you experience a strong up-currents. As every diver knows, to be swept up too fast is very dangerous (decompression sickness, lung damage) and should be avoided at all costs. I only experienced it once so far and it really scared me.
It was the beginning of the dive and we were at 30m, when the current started. It swept us up to 20m in no time, there we didn't see any alternative (no hiding places), so we grabbed onto the reef. There were some large dead coral pieces, they looked quite heavy, so I grabbed one. Even now it was extremely difficult, we were head down und were finning a lot. The current was so strong, that my octopus was ripped from the holder and started to freeflow behind my back. While I tried to grab it with one hand the coral piece in my other hand came loose (my camera was luckily attached to my jacket and wasn't even scratched!) and the current swept me away. I finned to get down to no avail, and went up much too fast from 18 to 8m and out in the blue - there was no way we could have gotten back to the reef. I did a really long safety stop but my computer still showed that I had gone up much too fast and needed several hours more surface interval. I felt lucky, I didn't get any decompression sickness!
Eddies: Washing machine / roller coaster:
These are my expressions for making somersaults in the water while trying to hold on to a piece of sponge or coral and trying to remember where the top and where the bottom is. I am watching my bubbles going down and out behind my back and then up in whirls and tornado shaped whorls. You won't need any fish indicators to know what it is. Actually you won't be able to see any fish, because you are just holding on for dear life!! (no photo available, I hope you understand!), just this illustration:
Sometimes there are a lot of fish together in an eddy up in the water column. These are usually good places to see a lot of large fish close-up - sometimes it is just a problem to get there, but it is a good place to be!
. Copyright Teresa Zubi (write to me)