What does the report say about the risk posed by microcystin?
The NLA conducted the first-ever national study of algal toxins in lakes. Microcystin – a toxin that can harm humans, pets and wildlife – was found to be present in about one third of lakes and at levels of concern in 1% of lakes. Using cyanbacteria cell counts as an indicator, approximately 27% of lakes nationwide pose a high or moderate risk for potential exposure to algal toxins. This could potentially have wide ranging impacts on human health and the swimmability of many lakes. When interpreting these data, however, it is important to keep in mind that the National Lakes Assessment relies on a single sample taken from the deepest water of each lake. • Cyanotoxin production varies throughout the summer, so the single sample may not represent the maximum concentration that was present. • Sampling in open water likely underestimates the true extent of toxin occurrence and magnitude. Winds are known to blow toxins to downwind shores. • One can’t assume there is no risk based on single
