And a Canadian report (not this article) reports that in the St Lawrence Basin the ag. land is fully saturated with phosphorus. "Our land is a sponge that can hold no more."
The article below suggests the problem just keeps growing (it is also better monitored).
https://www.ewg.org/agmag/2018/10/update-algae-outbreaks-rose-40-percent-2018#.W77miBQm2cs.twitter