I was snorkelling off north Cornwall in the red hot summer of '76. I stuck my head up to get my bearings - I was about 100yds off shore. I put my head in the water again, looked in front and there swaying towards me with the swell were about ten feet of Portuguese Man of War fronds. I had large scuba diving fins on, and as I hit the beach the cramps hit me and I rolled up in agony.