PlaceDossier / BC places / Lakes

BC lake · 5 km² · Victoria watershed

Shawnigan Lake

Its median summer total phosphorus over 2013–2025 was 4.3 µg/L, from 46 readings. Lower than 78% of the 100 BC lakes with enough recent readings (lower is clearer).

The readings

441 summer readings from open water on record from 1971 to 2025, at 13 sampling sites.

Median since 2012Compared with BC lakes
Secchi depthToo few readings to judge
16 readings since 2012, in 2 years		Too few readings to compare (16 readings since 2012, in 2 years).
Total phosphorus4.3 µg/L
2013–2025, 46 readings		Lower than 78% of the 100 BC lakes with enough recent readings (lower is clearer).
Chlorophyll aToo few readings to judge
16 readings since 2012, in 2 years		Too few readings to compare (16 readings since 2012, in 2 years).
Secchi depth how deep a black-and-white disc stays visible: deeper means clearer water
0246 19801990200020102020 1976: median 6.1 m from 5 readings1977: median 5.9 m from 15 readings1978: median 6.4 m from 13 readings1979: median 6.9 m from 4 readings1980: median 7.0 m from 3 readings1984: median 7.0 m from 1 reading1987: median 4.5 m from 1 reading2003: median 7.0 m from 22 readings2008: median 6.5 m from 16 readings2013: median 5.6 m from 8 readings2018: median 5.3 m from 8 readingsm
Total phosphorus the nutrient that most often feeds algae in BC lakes
31030 19801990200020102020 1971: median 3.5 µg/L from 2 readings1972: median 7.0 µg/L from 2 readings1973: median 5.0 µg/L from 1 reading1974: median 4.5 µg/L from 2 readings1975: median 3.0 µg/L from 1 reading1976: median 4.5 µg/L from 14 readings1977: median 5.0 µg/L from 34 readings1978: median 4.0 µg/L from 41 readings1979: median 6.0 µg/L from 6 readings1980: median 6.0 µg/L from 5 readings1981: median 8.0 µg/L from 1 reading1982: median 7.0 µg/L from 2 readings1983: median 6.0 µg/L from 1 reading1984: median 8.0 µg/L from 6 readings1987: median 7.0 µg/L from 2 readings1988: median 48 µg/L from 6 readings1991: median 3.0 µg/L from 1 reading2000: median 11 µg/L from 21 readings2001: median 2.0 µg/L from 7 readings2002: median 4.0 µg/L from 9 readings2003: median 4.0 µg/L from 38 readings2008: median 4.0 µg/L from 16 readings2013: median 4.0 µg/L from 18 readings2018: median 5.0 µg/L from 14 readings2024: median 3.5 µg/L from 6 readings2025: median 4.4 µg/L from 8 readingsµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
13 19801990200020102020 1977: median 2.3 µg/L from 8 readings1978: median 2.2 µg/L from 34 readings2003: median 1.8 µg/L from 4 readings2008: median 1.9 µg/L from 19 readings2013: median 2.9 µg/L from 8 readings2018: median 1.2 µg/L from 8 readingsµg/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

Reads as oligotrophic (few nutrients, little algae, usually clear).

IndexClass
From total phosphorus (4.3 µg/L, 2013–2025)25oligotrophic

Left out for too few recent readings (we need at least 10 summer readings from open water, spread over at least 3 different years, since 2012): secchi depth (16 readings since 2012, in 2 years); chlorophyll a (16 readings since 2012, in 2 years).

Inferred by us, not a provincial classification. 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.

How we worked this out

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.

Year by year

YearSecchi depthTotal phosphorusChlorophyll a
2025–4.4 µg/L (8)–
2024–3.5 µg/L (6)–
20185.3 m (8)5.0 µg/L (14)1.2 µg/L (8)
20135.6 m (8)4.0 µg/L (18)2.9 µg/L (8)
20086.5 m (16)4.0 µg/L (16)1.9 µg/L (19)
20037.0 m (22)4.0 µg/L (38)1.8 µg/L (4)
2002–4.0 µg/L (9)–
2001–2.0 µg/L (7)–
2000–11 µg/L (21)–
1991–3.0 µg/L (1)–
1988–48 µg/L (6)–
19874.5 m (1)7.0 µg/L (2)–
19847.0 m (1)8.0 µg/L (6)–
1983–6.0 µg/L (1)–
1982–7.0 µg/L (2)–
1981–8.0 µg/L (1)–
19807.0 m (3)6.0 µg/L (5)–
19796.9 m (4)6.0 µg/L (6)–
19786.4 m (13)4.0 µg/L (41)2.2 µg/L (34)
19775.9 m (15)5.0 µg/L (34)2.3 µg/L (8)
19766.1 m (5)4.5 µg/L (14)–
1975–3.0 µg/L (1)–
1974–4.5 µg/L (2)–
1973–5.0 µg/L (1)–
1972–7.0 µg/L (2)–
1971–3.5 µg/L (2)–

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

  • 1199901 #1 146 readings
  • 1199902 #2 114 readings
  • 1199903 West arm 68 readings
  • 1199904 #3 56 readings
  • 0131140 East side, north end 17 readings
  • 1199905 #4 12 readings
  • E222053 South end Swimming Area 5 readings
  • E294410 West arm - at outlet of Unnamed Trib 5 readings
  • E294413 D/s Cleared Hillside (Shaw 16) 5 readings
  • E315291 South basin deep point near Ssc Inflow (L1) 4 readings
  • E222041 West arm 3 readings
  • E222045 Galley Restaurant Area (Shaw 10) 3 readings
  • E246500 Mid basin at north end 3 readings

Left out: 17 readings at 3 sites whose names put them away from the open lake

  • E246900 Resort near dock (Shaw 13) 8 readings; on the shore
  • E222055 West Shawnigan Lake Provincial Park beach (Shaw 12) 6 readings; on the shore
  • E222048 Easter Seal Camp beach (Camp Shawnigan, Shaw 11) 3 readings; on the shore

Site names are tidied from the provincial records; 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. We leave out sites whose names put them at a water intake, a sewage or industrial outfall, a mine or a permit holder's works, or on the shore (a beach, dock or boat launch): water there can differ a lot from the open lake. Each year's figure is the median of that year's readings. We give a lake a summary, a comparison with other lakes and a nutrient level only when it has at least 10 summer readings from open water, spread over at least 3 different years, since 2012; the summary is the median of those readings. With fewer, or only older ones, we show the readings and say there are too few to judge the lake. 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.