What is the cleanest lake in British Columbia?

Quamichan Lake in Cowichan County is the highest-rated lake in British Columbia with an EPA water quality grade of NR and 5.6 feet of water clarity.

How are these rankings calculated?

Lakes are graded A through F on nutrients and algae — total phosphorus, nitrogen, chlorophyll-a, and turbidity — 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 Problems in British Columbia

6 lakes in British Columbia report elevated algae levels (chlorophyll-a above 20 µg/L). These lakes are most likely to develop blue-green algae blooms during warm, calm summer weather. Avoid swimming during visible blooms and rinse pets after contact.

Ranked List

#	Lake	County	Grade	Clarity	Phosphorus	Algae
1	Quamichan Lake	Cowichan	NR	5.6 ft	248 µg/L	46.7 µg/L
2	Michael Lake	Cowichan	NR	2.6 ft	11.5 µg/L	45.2 µg/L
3	Nulki Lake	Nechako River	NR	3.8 ft	97.6 µg/L	43.8 µg/L
4	Swan Lake	Victoria	NR	3.4 ft	219 µg/L	25.1 µg/L
5	Quennell Lake	Cowichan	NR	4.8 ft	61.9 µg/L	23.3 µg/L
6	Beaver Lake	Victoria	NR	-	25 µg/L	22 µg/L

Ranked List

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