Not much. Especially when considering the alternative of no action and its disastrous implications.
Our usage guidelines aim for treatment at the earliest stages, before the development of a massive bloom. This approach dramatically limits the treated area, keeps the needed dosage to the bare minimum and reduces the exposure of the aquatic fauna to unneeded algaecides on the one hand and cyanotoxins on the other.
Since the Lake Guard™ is designed to float and to slowly release its active compound, the actual chemical effect is physically limited to the surface of the water while keeping concentrations at minimal levels and enabling living organisms to find shelter, if needed at all, in deeper waters or simply upstream.