Killer sea foam?

Sadly, at least 5 surfers died in the Netherlands due to large waves and sea foam. details are light in the article, but wtf is killer sea foam?!? I've seen foam on lakes and rivers maybe 1' high in eddies or downwind side of lake, but never something that impairs visibility to the point of death and impaired rescue! have you seen or paddled in foam like this? where or when does it form? crazy.

condolences to the families

www.knrm.nl/nieuws/surfdrama-in-scheveningen

That is an awful tragedy. Startling that so many of the dead were very experienced lifeguards.

Killer sea foam?  Foam so deep that you can't see over it and can't get your head above it to breath. 

I've seen sea foam rapidly develop to huge quantities - when sailing a barge back from The Netherlands, the dutch toilet filled with foam. Amusing at first, then when the skipper opened the door to the heads and found the whole room filled (floor to ceiling) with foam, it became a problem. That was just sea foam churned in the dump-through toilet as the barge surged over waves. 

I can readily believe that the foam could have looked innocuous from the shore, then when paddling out it gets a bit more serious, get dumped off a wave, come up and your head is below the top of the foam. How do you breath then? How do you see the next dumping wave coming?

There is a lesson for all paddlers and surfers in this tragedy. 

I've experienced this regularly while surfing Sea Point (specifically Thermos) near Cape Town harbour. It's possibly the salinity levels of the water that cause the wave action to make the thick foam blanket on the surface. It's daunting to be caught in it, especially when it's more than a foot thick and you're trying to stretch your neck to get a clean breathe of air without burning the throat. I've an idea that there's something from harbours that cause it as I've also experienced this while surfing near Walvis Bay harbour. And Holland has one of the busiest harbours in the world at Rotterdam.