Why are the weeds stinging me

have been to two places lately and it seems that one of the plants in the water is stinging the crap out of me. Any idea's!!!!

I dont have a alergy to posion ivy but there is a alge in fresh water gives me the same effect I simply wash in cold water with ivory soap , make sure its cold water if I use hot it seems to spead once i do it gos away in a hour or so

Probably toxic slime in some of these ponds. May turn you into the swamp thing.