Largest Lakes in Ontario
We don't yet grade Ontario lakes for surface area. Browse all Ontario lakes for the data we do have.
Frequently Asked Questions
What is the largest lake in Ontario?
We don't yet grade Ontario lakes for surface area.
How is lake surface area measured?
Surface area comes from state DNR lake surveys and, for reservoirs, US Army Corps of Engineers (USACE) National Inventory of Dams records. Area is reported in acres at normal pool level. Reservoirs rise and fall with management and drought, so their listed area is the long-term normal rather than a single-day reading.
Are Ontario's largest lakes natural or reservoirs?
Reservoir vs natural breakdown is not available.
Do larger lakes have better water quality?
Not reliably. Quality varies more within a big lake than between lakes — a large lake can have a clean, deep main basin and a murky, algae-prone bay fed by a tributary, so one grade can mask wide swings. Depth, watershed land use, and how fast the lake flushes matter far more than raw surface area.
How big is the typical Ontario lake in this ranking?
Size summary not available.