PlaceDossier / BC places / Lakes

BC lake · 15 km² · Okanagan River watershed

Osoyoos Lake

Its median summer Secchi depth over 2012–2025 was 3.9 m, from 97 readings. Murkier than 64% of the 62 BC lakes with enough recent readings.

The readings

1,545 summer readings from open water on record from 1973 to 2026, at 14 sampling sites.

Median since 2012Compared with BC lakes
Secchi depth3.9 m
2012–2025, 97 readings		Murkier than 64% of the 62 BC lakes with enough recent readings.
Total phosphorus9.2 µg/L
2012–2026, 80 readings		Lower than 51% of the 100 BC lakes with enough recent readings (lower is clearer).
Chlorophyll a3.5 µg/L
2012–2026, 102 readings		Higher than 68% 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 19801990200020102020 1973: median 2.3 m from 2 readings1974: median 2.3 m from 2 readings1975: median 3.1 m from 5 readings1976: median 4.3 m from 6 readings1977: median 3.2 m from 6 readings1978: median 4.2 m from 7 readings1979: median 3.0 m from 7 readings1980: median 3.0 m from 8 readings1981: median 4.8 m from 3 readings1982: median 3.7 m from 3 readings1983: median 2.6 m from 2 readings1984: median 3.4 m from 2 readings1985: median 3.2 m from 2 readings1987: median 3.7 m from 2 readings1988: median 2.0 m from 2 readings1989: median 3.6 m from 2 readings1990: median 4.2 m from 1 reading1991: median 3.9 m from 2 readings1992: median 2.5 m from 2 readings1994: median 3.2 m from 32 readings1995: median 3.3 m from 35 readings1996: median 4.0 m from 32 readings1998: median 3.4 m from 4 readings1999: median 3.4 m from 64 readings2000: median 3.8 m from 47 readings2001: median 3.6 m from 54 readings2002: median 3.5 m from 79 readings2003: median 3.5 m from 85 readings2004: median 3.4 m from 82 readings2006: median 2.7 m from 55 readings2007: median 3.7 m from 4 readings2009: median 3.4 m from 16 readings2010: median 3.3 m from 16 readings2011: median 3.2 m from 14 readings2012: median 3.6 m from 15 readings2013: median 4.0 m from 14 readings2014: median 3.7 m from 13 readings2015: median 4.2 m from 25 readings2016: median 3.5 m from 3 readings2017: median 4.7 m from 3 readings2018: median 3.8 m from 3 readings2019: median 4.1 m from 3 readings2020: median 5.0 m from 3 readings2021: median 4.5 m from 3 readings2022: median 4.4 m from 3 readings2023: median 3.3 m from 3 readings2024: median 3.4 m from 3 readings2025: median 3.6 m from 3 readingsm
Total phosphorus the nutrient that most often feeds algae in BC lakes
1030 19801990200020102020 1974: median 13 µg/L from 2 readings1975: median 17 µg/L from 5 readings1976: median 13 µg/L from 11 readings1977: median 15 µg/L from 12 readings1978: median 14 µg/L from 12 readings1979: median 17 µg/L from 8 readings1980: median 20 µg/L from 7 readings1981: median 17 µg/L from 3 readings1982: median 20 µg/L from 3 readings1983: median 17 µg/L from 2 readings1984: median 19 µg/L from 2 readings1985: median 18 µg/L from 2 readings1986: median 13 µg/L from 2 readings1987: median 16 µg/L from 2 readings1988: median 20 µg/L from 2 readings1989: median 12 µg/L from 3 readings1990: median 11 µg/L from 2 readings1991: median 9.0 µg/L from 2 readings1992: median 32 µg/L from 2 readings1993: median 9.0 µg/L from 7 readings1994: median 11 µg/L from 57 readings1995: median 12 µg/L from 3 readings1998: median 14 µg/L from 2 readings1999: median 15 µg/L from 4 readings2000: median 17 µg/L from 4 readings2001: median 13 µg/L from 18 readings2002: median 12 µg/L from 18 readings2003: median 8.0 µg/L from 9 readings2004: median 13 µg/L from 9 readings2005: median 8.0 µg/L from 17 readings2006: median 6.0 µg/L from 9 readings2007: median 11 µg/L from 5 readings2008: median 9.0 µg/L from 10 readings2009: median 7.0 µg/L from 19 readings2010: median 8.0 µg/L from 10 readings2011: median 6.5 µg/L from 10 readings2012: median 11 µg/L from 9 readings2013: median 10 µg/L from 8 readings2014: median 7.6 µg/L from 8 readings2015: median 7.4 µg/L from 23 readings2016: median 12 µg/L from 3 readings2017: median 5.0 µg/L from 3 readings2018: median 12 µg/L from 3 readings2019: median 9.4 µg/L from 3 readings2020: median 13 µg/L from 3 readings2021: median 12 µg/L from 3 readings2022: median 16 µg/L from 3 readings2023: median 13 µg/L from 3 readings2024: median 9.8 µg/L from 3 readings2025: median 9.8 µg/L from 3 readings2026: median 13 µg/L from 2 readingsµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
1310 19801990200020102020 1975: median 5.6 µg/L from 2 readings1976: median 4.3 µg/L from 18 readings1977: median 4.8 µg/L from 17 readings1978: median 4.2 µg/L from 18 readings1979: median 6.9 µg/L from 10 readings1980: median 5.6 µg/L from 8 readings1981: median 4.9 µg/L from 3 readings1982: median 3.5 µg/L from 4 readings1983: median 7.0 µg/L from 2 readings1984: median 5.6 µg/L from 2 readings1987: median 0.5 µg/L from 1 reading1988: median 8.6 µg/L from 2 readings1989: median 6.7 µg/L from 3 readings1990: median 5.0 µg/L from 2 readings1991: median 8.4 µg/L from 2 readings1992: median 13 µg/L from 2 readings1993: median 5.0 µg/L from 3 readings1994: median 6.5 µg/L from 27 readings1996: median 3.4 µg/L from 2 readings1998: median 4.4 µg/L from 4 readings1999: median 5.9 µg/L from 4 readings2000: median 3.6 µg/L from 8 readings2001: median 3.0 µg/L from 18 readings2002: median 5.0 µg/L from 14 readings2003: median 5.5 µg/L from 5 readings2004: median 4.3 µg/L from 9 readings2005: median 4.4 µg/L from 9 readings2006: median 4.1 µg/L from 13 readings2007: median 4.0 µg/L from 12 readings2008: median 3.7 µg/L from 16 readings2009: median 4.2 µg/L from 16 readings2010: median 3.8 µg/L from 16 readings2011: median 2.9 µg/L from 14 readings2012: median 2.8 µg/L from 15 readings2013: median 3.8 µg/L from 15 readings2014: median 3.6 µg/L from 13 readings2015: median 2.6 µg/L from 27 readings2016: median 4.6 µg/L from 3 readings2017: median 4.3 µg/L from 3 readings2018: median 6.8 µg/L from 3 readings2019: median 4.6 µg/L from 3 readings2020: median 3.0 µg/L from 3 readings2021: median 2.8 µg/L from 3 readings2022: median 4.7 µg/L from 3 readings2023: median 4.3 µg/L from 3 readings2024: median 5.4 µg/L from 3 readings2025: median 2.6 µg/L from 3 readings2026: median 9.1 µg/L from 2 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

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

IndexClass
From secchi depth (3.9 m, 2012–2025)40mesotrophic
From total phosphorus (9.2 µg/L, 2012–2026)36oligotrophic
From chlorophyll a (3.5 µg/L, 2012–2026)43mesotrophic

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
2026–13 µg/L (2)9.1 µg/L (2)
20253.6 m (3)9.8 µg/L (3)2.6 µg/L (3)
20243.4 m (3)9.8 µg/L (3)5.4 µg/L (3)
20233.3 m (3)13 µg/L (3)4.3 µg/L (3)
20224.4 m (3)16 µg/L (3)4.7 µg/L (3)
20214.5 m (3)12 µg/L (3)2.8 µg/L (3)
20205.0 m (3)13 µg/L (3)3.0 µg/L (3)
20194.1 m (3)9.4 µg/L (3)4.6 µg/L (3)
20183.8 m (3)12 µg/L (3)6.8 µg/L (3)
20174.7 m (3)5.0 µg/L (3)4.3 µg/L (3)
20163.5 m (3)12 µg/L (3)4.6 µg/L (3)
20154.2 m (25)7.4 µg/L (23)2.6 µg/L (27)
20143.7 m (13)7.6 µg/L (8)3.6 µg/L (13)
20134.0 m (14)10 µg/L (8)3.8 µg/L (15)
20123.6 m (15)11 µg/L (9)2.8 µg/L (15)
20113.2 m (14)6.5 µg/L (10)2.9 µg/L (14)
20103.3 m (16)8.0 µg/L (10)3.8 µg/L (16)
20093.4 m (16)7.0 µg/L (19)4.2 µg/L (16)
2008–9.0 µg/L (10)3.7 µg/L (16)
20073.7 m (4)11 µg/L (5)4.0 µg/L (12)
20062.7 m (55)6.0 µg/L (9)4.1 µg/L (13)
2005–8.0 µg/L (17)4.4 µg/L (9)
20043.4 m (82)13 µg/L (9)4.3 µg/L (9)
20033.5 m (85)8.0 µg/L (9)5.5 µg/L (5)
20023.5 m (79)12 µg/L (18)5.0 µg/L (14)
20013.6 m (54)13 µg/L (18)3.0 µg/L (18)
20003.8 m (47)17 µg/L (4)3.6 µg/L (8)
19993.4 m (64)15 µg/L (4)5.9 µg/L (4)
19983.4 m (4)14 µg/L (2)4.4 µg/L (4)
19964.0 m (32)–3.4 µg/L (2)
19953.3 m (35)12 µg/L (3)–
19943.2 m (32)11 µg/L (57)6.5 µg/L (27)
1993–9.0 µg/L (7)5.0 µg/L (3)
19922.5 m (2)32 µg/L (2)13 µg/L (2)
19913.9 m (2)9.0 µg/L (2)8.4 µg/L (2)
19904.2 m (1)11 µg/L (2)5.0 µg/L (2)
19893.6 m (2)12 µg/L (3)6.7 µg/L (3)
19882.0 m (2)20 µg/L (2)8.6 µg/L (2)
19873.7 m (2)16 µg/L (2)0.5 µg/L (1)
1986–13 µg/L (2)–
19853.2 m (2)18 µg/L (2)–
19843.4 m (2)19 µg/L (2)5.6 µg/L (2)
19832.6 m (2)17 µg/L (2)7.0 µg/L (2)
19823.7 m (3)20 µg/L (3)3.5 µg/L (4)
19814.8 m (3)17 µg/L (3)4.9 µg/L (3)
19803.0 m (8)20 µg/L (7)5.6 µg/L (8)
19793.0 m (7)17 µg/L (8)6.9 µg/L (10)
19784.2 m (7)14 µg/L (12)4.2 µg/L (18)
19773.2 m (6)15 µg/L (12)4.8 µg/L (17)
19764.3 m (6)13 µg/L (11)4.3 µg/L (18)
19753.1 m (5)17 µg/L (5)5.6 µg/L (2)
19742.3 m (2)13 µg/L (2)–
19732.3 m (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

  • 0500728 Opposite Monashee Co-Op 571 readings
  • 0500249 North end 357 readings
  • 0500248 South basin 303 readings
  • E220540 Central basin 269 readings
  • 0500452 . near mouth Okanagan River 36 readings
  • E221954 At Haynes Point Provincial Park 1 reading
  • E221955 At Sailing Club 1 reading
  • E221956 At 164TH St 1 reading
  • E276526 (OSN-2) 1 km Se of Willow beach, Sw of 0500249 1 reading
  • E276527 (OSN-3) 175 m Nw of Inkaneep Rd, opposite Inkaneep Creek 1 reading
  • E276528 (OSN-4) 275 m Ne of 150TH Ave 1 reading
  • E276529 (OSN-5) 90 m Se of Monashee Co-Op Building 1 reading
  • E276530 (ONS-6) 170 m Ne of 98TH Ave 1 reading
  • E276532 (OSC-1) south of Mainstreet at east end of Park 1 reading

Left out: 4 readings at 4 sites whose names put them away from the open lake

  • E276525 (OSN-1) west end of Willow beach 1 reading; on the shore
  • E276531 (OSN-7) at Boat Launch north of Sailing Club 1 reading; on the shore
  • E276533 (OSC-2) north shore of Haynes Point Prov. Park 1 reading; on the shore
  • E276534 Osoyoos Lkk (OSS-1) south shore of Haynes Point Prov. Park 1 reading; 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.