The positive test in an algal mat for Anatoxin-A (ATX) downstream from the found family was 11.8 µg/L. Algal mats can be positive for 1,000s of units, so that level is low, not high as the media states.
https://mywaterquality.ca.gov/habs/where/freshwater_events.htmlThe WHO, in their Guidelines on Recreational Water Quality, 2021, gives a WHO guideline value (GV)recreation for Anatoxin A at a level of WHO HBVrecreation = 60 µg/L
(For ATXs, toxicological data were insufficient for deriving a guideline value, but allow deriving an upper bounding value below which health impacts are highly unlikely – that is, a health-based value.)
https://www.ncbi.nlm.nih.gov/books/NBK572631/Some municipal waters allow ATX at levels of 20 µg/L (Ohio at that level only puts out advisory)
https://en.wikipedia.org/wiki/Anatoxin-a
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