PlaceDossier / BC places / Lakes

BC lake · 3 km² · Cowichan watershed

Quamichan Lake

Its median summer Secchi depth over 2016–2025 was 1.0 m, from 10 readings. Murkier than 98% of the 122 BC lakes with at least 5 readings.

The readings

113 summer readings on record from 1988 to 2026, at 3 sampling sites.

Median, latest 10 sampled yearsCompared with BC lakes
Secchi depth1.0 m
2016–2025, 10 readings		Murkier than 98% of the 122 BC lakes with at least 5 readings.
Total phosphorus282 µg/L
2017–2026, 17 readings		Higher than 99% of the 269 BC lakes with at least 5 readings.
Chlorophyll a58 µg/L
2017–2026, 10 readings		Higher than 100% of the 156 BC lakes with at least 5 readings.
Secchi depth how deep a black-and-white disc stays visible: deeper means clearer water
0246 1990200020102020 2004: median 3.5 m from 2 readings2005: median 1.5 m from 1 reading2007: median 2.2 m from 3 readings2015: median 0.4 m from 1 reading2016: median 1.1 m from 1 reading2017: median 0.9 m from 1 reading2018: median 1.1 m from 1 reading2019: median 2.1 m from 1 reading2020: median 0.8 m from 1 reading2021: median 0.2 m from 1 reading2022: median 1.2 m from 1 reading2023: median 0.5 m from 1 reading2024: median 0.8 m from 1 reading2025: median 1.6 m from 1 readingm
Total phosphorus the nutrient that most often feeds algae in BC lakes
1030100300 1990200020102020 1988: median 245 µg/L from 26 readings1992: median 92 µg/L from 12 readings2001: median 22 µg/L from 3 readings2004: median 108 µg/L from 1 reading2005: median 66 µg/L from 3 readings2006: median 39 µg/L from 3 readings2007: median 76 µg/L from 3 readings2015: median 376 µg/L from 4 readings2016: median 298 µg/L from 1 reading2017: median 435 µg/L from 8 readings2018: median 347 µg/L from 1 reading2019: median 282 µg/L from 1 reading2020: median 297 µg/L from 1 reading2021: median 145 µg/L from 1 reading2022: median 91 µg/L from 1 reading2023: median 237 µg/L from 1 reading2024: median 172 µg/L from 1 reading2025: median 133 µg/L from 1 reading2026: median 177 µg/L from 1 readingµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
131030100 1990200020102020 2004: median 2.8 µg/L from 1 reading2005: median 21 µg/L from 1 reading2006: median 5.2 µg/L from 3 readings2007: median 42 µg/L from 4 readings2015: median 40 µg/L from 3 readings2016: median 33 µg/L from 1 reading2017: median 45 µg/L from 1 reading2018: median 23 µg/L from 1 reading2019: median 30 µg/L from 1 reading2020: median 53 µg/L from 1 reading2021: median 62 µg/L from 1 reading2022: median 54 µg/L from 1 reading2023: median 95 µg/L from 1 reading2024: median 103 µg/L from 1 reading2025: median 133 µg/L from 1 reading2026: median 119 µg/L from 1 readingµg/L

Median each year (bigger dot, more readings)Middle half of BC lakesBC median

Source: BC Environmental Monitoring Data System (EnMoDS) results, Environmental Monitoring and Analysis Branch, Province of BC, records to September 19, 2026 (Open Government Licence – British Columbia); lake outlines and names: Freshwater Atlas lakes, Province of BC (Open Government Licence – British Columbia). Summaries by PlaceDossier.

Nutrient level Inferred

The measures disagree: clarity reads eutrophic, phosphorus reads hypereutrophic, algae reads hypereutrophic. That's common: clarity also depends on silt and colour, not just algae.

IndexClass
From secchi depth (1.0 m, 2016–2025)60eutrophic
From total phosphorus (282 µg/L, 2017–2026)86hypereutrophic
From chlorophyll a (58 µg/L, 2017–2026)70hypereutrophic

Inferred by us, not a provincial classification. Carlson's trophic state index (Carlson 1977, Limnology and Oceanography 22:361) turns each median into a score: 60 − 14.41 ln(Secchi m), 14.42 ln(phosphorus µg/L) + 4.15, 9.81 ln(chlorophyll µg/L) + 30.6. Classes after Carlson and Simpson (1996): under 40 oligotrophic, 40 to 50 mesotrophic, 50 to 70 eutrophic, 70 and over hypereutrophic. The index was built for summer readings from the middle of a lake; ours mix sites and months, so treat the class as a rough guide.

Year by year

YearSecchi depthTotal phosphorusChlorophyll a
2026–177 µg/L (1)119 µg/L (1)
20251.6 m (1)133 µg/L (1)133 µg/L (1)
20240.8 m (1)172 µg/L (1)103 µg/L (1)
20230.5 m (1)237 µg/L (1)95 µg/L (1)
20221.2 m (1)91 µg/L (1)54 µg/L (1)
20210.2 m (1)145 µg/L (1)62 µg/L (1)
20200.8 m (1)297 µg/L (1)53 µg/L (1)
20192.1 m (1)282 µg/L (1)30 µg/L (1)
20181.1 m (1)347 µg/L (1)23 µg/L (1)
20170.9 m (1)435 µg/L (8)45 µg/L (1)
20161.1 m (1)298 µg/L (1)33 µg/L (1)
20150.4 m (1)376 µg/L (4)40 µg/L (3)
20072.2 m (3)76 µg/L (3)42 µg/L (4)
2006–39 µg/L (3)5.2 µg/L (3)
20051.5 m (1)66 µg/L (3)21 µg/L (1)
20043.5 m (2)108 µg/L (1)2.8 µg/L (1)
2001–22 µg/L (3)–
1992–92 µg/L (12)–
1988–245 µg/L (26)–

Median of each year's May to October readings; the number of readings is in brackets.

Source: BC Environmental Monitoring Data System (EnMoDS) results, Environmental Monitoring and Analysis Branch, Province of BC, records to September 19, 2026 (Open Government Licence – British Columbia); lake outlines and names: Freshwater Atlas lakes, Province of BC (Open Government Licence – British Columbia). Summaries by PlaceDossier.

Where it was sampled

  • E207465 QUAMICHAN LAKE; 0.5 KM SOUTH OF CENTRE 99 readings
  • E207466 QUAMICHAN LAKE; CENTRE 89 readings
  • E309288 QUAMICHAN LAKE NEAR STAMPS ROAD 10 readings

Site names and IDs are as recorded in the provincial database; the IDs find each site's full record there.

What this record doesn't cover

Algae bloom reports and invasive mussel checks aren't in this record: the province's Algae Watch map and mussel monitoring aren't published as open data. For swimming, check the regional health authority's beach advisories; for blooms and mussels, ask the province's regional environment office or the local lake association.

Readings are from the province's monitoring database: samples taken by provincial staff, volunteer lake monitors, and companies and local governments that sample under their permits. We keep the ice-free season (May to October), and for phosphorus and chlorophyll only samples from the top 5 m. Each year's figure is the median of that year's readings; the summary is the median of every reading in the lake's latest 10 sampled years. A reading below the lab's detection limit counts at that limit. One site can be a bay rather than the open lake, so a lake's figures can differ from one end to the other.

Water quality changes with the season, the weather and the part of the lake. These are past readings, not a test of the water today: before you buy, ask the local government and the lake association what's known, and test a drinking-water intake yourself.