Beware of Dangerous Downcurrents

By John Lippmann, Founder, Chairman & Director of Research, DAN World

Currents that present the greatest risk to divers run downwards or upwards and are often caused when a horizontal current hits an underwater “wall”. Dangerously, divers can be unexpectedly dragged to depth and risk running out of breathing gas and/or having very rapid ascents when released by the currents. Knowledge and skills to prevent or minimise the problem are vital for all divers, given the number of divers who travel to destinations of which they have little local knowledge and supervision, if available, may be of a variable standard.

It was interesting to read a while ago that the local police had temporarily banned diving at Crystal Bay, Nusa Penida in Bali. This was to investigate why so many diving-related deaths had been occurring there. It is a popular diving site due to the periodic presence of Sunfish (Mola Mola). However, there are some serious potential hazards there for divers, especially inexperienced and/or unwary divers.

The area is subject to very strong currents, including substantial downcurrents which can suddenly force a diver to descend far deeper than planned - and quickly. The Sunfish are often already quite deep so this has caused numerous accidents, including multiple deaths and severe cases of decompression illness. Divers can be unexpectedly dragged to depth and run out of breathing gas and/or have very rapid ascents when released by the currents.

Such downcurrents occur regularly in a variety of sites around the world, but the majority of reports DAN World has received over the past few years has been from Indonesia; predominantly Nusa Penida, the Komodo area, Raja Ampat and Bunaken. These have become popular destinations for divers due to the rich and diverse marine life. However, unfortunately the safety standards and preparedness of dive operators varies greatly and unsuspecting divers sometimes find themselves in perilous situations.

Most currents run horizontally across the earth’s surface. Divers can, and do, occasionally get stranded and sometimes lost at sea as a result of these. However, the currents that present the greatest risk to divers run downwards or upwards and are often caused when a horizontal current hits an underwater “wall” and is then forced to flow downwards, or upwards.

The strength of the current will vary with the tide and conditions. There is often no obvious sign of the presence of such a current, although there can sometimes be a rippling and/or swirling on the surface in the area. Therefore, local knowledge is very important and experienced local divers are usually a good source of information.

To Prevent or Minimise the Problem:

  • If diving independently, get good local knowledge about the planned dive site.
  • If diving with an operator, choose them carefully.
  • Ask specific questions about prevailing currents as well as other potential hazards.
  • Be aware of your location throughout the dive.
  • If close to a wall when caught in an up-current or down-current, try to grab or hook onto the wall to avoid being swept away.
  • If unable to get a hold on the wall, swim away from it as the current should lessen further away.
  • If you are being dragged down:
    - keep calm
    - equalise your ears as necessary
    - inflate your BCD
    - swim up & away from the wall
    - if you have no visual reference, watch your bubbles for orientation (although this can sometimes be misleading in a strong downcurrent).
    - monitor your breathing gas
  • If you are being dragged upwards:
    - keep calm
    - swim down & away from the wall
    - deflate your BCD
    - exhale appropriately and then continue to breathe as appropriate
    - spread your arms and legs to slow the ascent.  

Diving in current can be very rewarding due to the rich marine life often associated with them and the wide territory than can sometimes be covered with little effort. However, adequate preparedness is essential to maximise enjoyment and safety. 

Safe Diving,

John Lippmann
DAN World