I know there's not much one can do, save, accept that Jellyfish are part of the ocean's architecture - but they do seem to be proliferating in the area just now.
Since moving to Amlan 2 months ago, I have been out snorkelling most days and have noticed a dramatic increase in jellyfish over the last week or so. After some handy Google research I understand that 'peak season' for Jellyfish (Philippines) is April-May - which coincides with their earlier spawning season and feeding habits chasing Plankton etc. I have also learnt that although saltwater habitants, most favour egg laying in areas where fresh water rivers/streams converge with the sea - of which there are many opportunities in the DC (and surrounding) areas.
Box Jellyfish seem to be quite common in the Philippines too, although not usually as gargantuan in size as their Australian counterparts. Although stings from Box Jellyfish should not be treated with vinegar (or your best friend happily 'taking a leak' over the effected area) - one exception seems to be:
(Interesting factoid) : Filipino homemade coconut vinegar - which apparently does help to reduce additional venom from the stings entering the body/bloodstream. For this reason, many 'locals' carry a small bottle of coconut vinegar in their boats and pour it over the effected area (without rubbing obviously!!) Then scrape the area gently with a knife or credit card-type object to remove any remaining stings from the surface of the skin. It is recommended that medical treatment is sought, even if the injured party feels OK, as 'toxic shock' can occur up to 48 hours after the event. Usually anti-inflamatories/histamines do the trick, although permanent 'battle scarring' is common.
I'm not Jacques Cousteau, a Nurse or a Witch Doctor; but I thought the above findings might be of interest to others as, of late, there seems to be many more Jellyfish in the vicinity.
It is worth pointing out of course that the vast majority of these critters are relatively harmless, save some minor discomfort for a couple of hours after being stung.