PlaceDossier / BC places / Lakes

BC lake · 7 km² · San Jose River watershed

Williams Lake

Its median summer Secchi depth over 2017–2025 was 1.2 m, from 10 readings. Murkier than 97% of the 62 BC lakes with enough recent readings.

The readings

223 summer readings from open water on record from 1985 to 2026, at 2 sampling sites.

Median since 2012Compared with BC lakes
Secchi depth1.2 m
2017–2025, 10 readings		Murkier than 97% of the 62 BC lakes with enough recent readings.
Total phosphorus28 µg/L
2012–2026, 18 readings		Higher than 84% of the 100 BC lakes with enough recent readings.
Chlorophyll a13 µg/L
2012–2026, 14 readings		Higher than 95% of the 83 BC lakes with enough recent readings.
Secchi depth how deep a black-and-white disc stays visible: deeper means clearer water
0246 1990200020102020 1988: median 1.0 m from 1 reading1989: median 1.6 m from 4 readings1990: median 2.6 m from 26 readings1991: median 2.0 m from 4 readings1993: median 2.3 m from 25 readings1994: median 1.9 m from 3 readings2017: median 0.8 m from 1 reading2018: median 1.5 m from 1 reading2019: median 1.3 m from 1 reading2020: median 1.3 m from 1 reading2021: median 1.1 m from 1 reading2022: median 1.2 m from 1 reading2023: median 1.1 m from 2 readings2024: median 1.0 m from 1 reading2025: median 1.5 m from 1 readingm
Total phosphorus the nutrient that most often feeds algae in BC lakes
1030100 1990200020102020 1985: median 35 µg/L from 1 reading1987: median 30 µg/L from 5 readings1988: median 24 µg/L from 5 readings1989: median 28 µg/L from 6 readings1990: median 33 µg/L from 12 readings1991: median 35 µg/L from 7 readings1992: median 24 µg/L from 5 readings1996: median 27 µg/L from 4 readings2004: median 22 µg/L from 18 readings2005: median 31 µg/L from 16 readings2006: median 15 µg/L from 11 readings2011: median 41 µg/L from 3 readings2012: median 57 µg/L from 3 readings2015: median 18 µg/L from 2 readings2016: median 23 µg/L from 1 reading2017: median 28 µg/L from 1 reading2018: median 27 µg/L from 1 reading2019: median 28 µg/L from 1 reading2020: median 28 µg/L from 1 reading2021: median 27 µg/L from 1 reading2022: median 28 µg/L from 1 reading2023: median 55 µg/L from 2 readings2024: median 27 µg/L from 1 reading2025: median 26 µg/L from 1 reading2026: median 86 µg/L from 2 readingsµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
131030 1990200020102020 1985: median 15 µg/L from 1 reading1987: median 10 µg/L from 2 readings1988: median 18 µg/L from 1 reading1989: median 19 µg/L from 1 reading1995: median 8.8 µg/L from 6 readings1996: median 11 µg/L from 8 readings2006: median 34 µg/L from 5 readings2011: median 20 µg/L from 1 reading2012: median 11 µg/L from 1 reading2015: median 4.6 µg/L from 1 reading2016: median 12 µg/L from 1 reading2017: median 15 µg/L from 1 reading2018: median 9.7 µg/L from 1 reading2019: median 16 µg/L from 1 reading2020: median 26 µg/L from 1 reading2021: median 14 µg/L from 1 reading2022: median 22 µg/L from 1 reading2023: median 14 µg/L from 2 readings2024: median 13 µg/L from 1 reading2025: median 13 µg/L from 1 reading2026: median 4.8 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

Reads as eutrophic (rich in nutrients, with more algae and weed growth).

IndexClass
From secchi depth (1.2 m, 2017–2025)58eutrophic
From total phosphorus (28 µg/L, 2012–2026)52eutrophic
From chlorophyll a (13 µg/L, 2012–2026)56eutrophic

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
2026–86 µg/L (2)4.8 µg/L (1)
20251.5 m (1)26 µg/L (1)13 µg/L (1)
20241.0 m (1)27 µg/L (1)13 µg/L (1)
20231.1 m (2)55 µg/L (2)14 µg/L (2)
20221.2 m (1)28 µg/L (1)22 µg/L (1)
20211.1 m (1)27 µg/L (1)14 µg/L (1)
20201.3 m (1)28 µg/L (1)26 µg/L (1)
20191.3 m (1)28 µg/L (1)16 µg/L (1)
20181.5 m (1)27 µg/L (1)9.7 µg/L (1)
20170.8 m (1)28 µg/L (1)15 µg/L (1)
2016–23 µg/L (1)12 µg/L (1)
2015–18 µg/L (2)4.6 µg/L (1)
2012–57 µg/L (3)11 µg/L (1)
2011–41 µg/L (3)20 µg/L (1)
2006–15 µg/L (11)34 µg/L (5)
2005–31 µg/L (16)–
2004–22 µg/L (18)–
1996–27 µg/L (4)11 µg/L (8)
1995––8.8 µg/L (6)
19941.9 m (3)––
19932.3 m (25)––
1992–24 µg/L (5)–
19912.0 m (4)35 µg/L (7)–
19902.6 m (26)33 µg/L (12)–
19891.6 m (4)28 µg/L (6)19 µg/L (1)
19881.0 m (1)24 µg/L (5)18 µg/L (1)
1987–30 µg/L (5)10 µg/L (2)
1985–35 µg/L (1)15 µg/L (1)

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

  • 0603019 At centre 211 readings
  • 0603022 At deepest point 12 readings

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.