The dose is 1000mg. You may remember that a few years ago, there were local problems with cyanobacteria. They pose a hazard in hot, especially bright, summers in tranquil freshwater environments. Not all species are toxic but those that are produce hepatotoxins and neurotoxins. There is no clear link between the composition and density of a bloom and the toxins deriving therefrom.
Cyanobacteria form blue-green, blue, green or dark brown blooms.
Outbreaks of gastroenteritis and subclinical hepatitis have followed consumption of contaminated water. Cyanobacteria can be demonstrated on microscopy of faeces. There is no specific treatment. If you think that you have found a case, please let me know so that control measures can be instituted. There was a rapid rise in Shigellosis in East Anglia in 1992 to 400 compared with an average for the preceding decade of a little over 50.