The State of Ontario’s Lakes 2026

Cleanest lakes in Ontario

Highest combined water-quality score, 2026.

1. 1.ACrosby Lake — Leeds and Grenville Counties County17.1 ft clarity · 10 µg/L P
2. 2.AAllen Lake — Haliburton County19.4 ft clarity · 5 µg/L P
3. 3.AAnimoosh Lake — Nipissing District County15.6 ft clarity · 12 µg/L P
4. 4.AAnstruther Lake — Peterborough County16.4 ft clarity · 6 µg/L P
5. 5.AArdoch Lake — Frontenac County19.0 ft clarity · 7 µg/L P
6. 6.AArmstrong Lake — Sudbury District County15.1 ft clarity · 6 µg/L P
7. 7.AArnott Lake — Algoma District County24.0 ft clarity · 5 µg/L P
8. 8.AArrow Lake — Thunder Bay District County24.0 ft clarity · 8 µg/L P
9. 9.AAylen Lake — Nipissing District County17.9 ft clarity · 3 µg/L P
10. 10.ABagot Long Lake — Renfrew County15.1 ft clarity · 14 µg/L P

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

1. 1.FAlder Lake — Region of Waterloo County1.6 ft clarity · 148 µg/L P
2. 2.DAbitibi Lake — Cochrane District County1.0 ft clarity · 62 µg/L P
3. 3.DGrenadier Pond — Golden Horseshoe County3.3 ft clarity · 63 µg/L P
4. 4.DBlack River Lake — Cochrane District County1.6 ft clarity · 38 µg/L P
5. 5.DColonel by Lake — Eastern Ontario County1.6 ft clarity · 44 µg/L P
6. 6.DCox Lake — Thunder Bay District County2.0 ft clarity · 51 µg/L P
7. 7.DGibboney Lake — Algoma District County3.3 ft clarity · 41 µg/L P
8. 8.DSkeleton Lake — Timiskaming District County2.0 ft clarity · 33 µg/L P
9. 9.DWistiwasing Lake — Nipissing District County3.0 ft clarity · 32 µg/L P
10. 10.DFanshawe Lake — Middlesex County2.6 ft clarity · 46 µg/L P

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

No qualifying lakes with sufficient data.