How are these rankings calculated?

Nutrients and algae, total phosphorus, nitrogen, chlorophyll-a and turbidity, are read against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown; it is not the letter. Lakes without enough recent samples are UNRATED, not given an F. Source data comes from the EPA Water Quality Portal.

Lakes With Algae Readings in Ontario

No monitored lake in Ontario is above the 20 ug/L chlorophyll-a threshold in the available readings. That is not an all-clear: many lakes are unmonitored, readings lag by weeks, and blooms develop in days. Check state advisories before you swim.

More Answers for Ontario