PlaceDossier / BC places / Lakes

BC lake · 67 km² · Bull River watershed

Lake Koocanusa

Its median summer Secchi depth over 2015–2026 was 2.1 m, from 997 readings. Murkier than 87% of the 62 BC lakes with enough recent readings.

The readings

7,282 summer readings from open water on record from 1972 to 2026, at 23 sampling sites.

Median since 2012Compared with BC lakes
Secchi depth2.1 m
2015–2026, 997 readings		Murkier than 87% of the 62 BC lakes with enough recent readings.
Total phosphorus6.2 µg/L
2015–2026, 3,281 readings		Lower than 63% of the 100 BC lakes with enough recent readings (lower is clearer).
Chlorophyll a1.2 µg/L
2015–2026, 2,731 readings		Lower than 70% of the 83 BC lakes with enough recent readings (lower is clearer).
Secchi depth how deep a black-and-white disc stays visible: deeper means clearer water
0246 19801990200020102020 1972: median 1.1 m from 1 reading1973: median 2.3 m from 4 readings1974: median 6.1 m from 19 readings1975: median 3.8 m from 9 readings1976: median 4.3 m from 10 readings1977: median 1.2 m from 5 readings1978: median 4.8 m from 8 readings1979: median 3.8 m from 8 readings1980: median 3.7 m from 13 readings2015: median 3.6 m from 20 readings2016: median 2.7 m from 73 readings2017: median 1.1 m from 70 readings2018: median 2.6 m from 63 readings2019: median 1.6 m from 70 readings2020: median 1.0 m from 72 readings2021: median 1.3 m from 70 readings2022: median 4.0 m from 83 readings2023: median 3.2 m from 160 readings2024: median 2.0 m from 126 readings2025: median 2.6 m from 130 readings2026: median 0.6 m from 60 readingsm
Total phosphorus the nutrient that most often feeds algae in BC lakes
31030100300 19801990200020102020 1972: median 65 µg/L from 2 readings1973: median 231 µg/L from 6 readings1974: median 9.0 µg/L from 11 readings1975: median 49 µg/L from 9 readings1976: median 9.0 µg/L from 11 readings1977: median 13 µg/L from 7 readings1978: median 7.5 µg/L from 10 readings1979: median 10 µg/L from 13 readings1980: median 10 µg/L from 15 readings2008: median 4.0 µg/L from 9 readings2015: median 5.3 µg/L from 190 readings2016: median 6.5 µg/L from 202 readings2017: median 11 µg/L from 164 readings2018: median 9.1 µg/L from 251 readings2019: median 5.3 µg/L from 239 readings2020: median 7.2 µg/L from 250 readings2021: median 7.0 µg/L from 259 readings2022: median 6.9 µg/L from 311 readings2023: median 5.3 µg/L from 449 readings2024: median 5.9 µg/L from 464 readings2025: median 5.1 µg/L from 424 readings2026: median 18 µg/L from 78 readingsµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
13 19801990200020102020 1975: median 4.4 µg/L from 14 readings1976: median 1.5 µg/L from 18 readings1977: median 2.8 µg/L from 10 readings1978: median 1.2 µg/L from 17 readings1979: median 1.3 µg/L from 20 readings1980: median 1.2 µg/L from 24 readings2015: median 1.0 µg/L from 72 readings2016: median 0.9 µg/L from 202 readings2017: median 0.5 µg/L from 167 readings2018: median 1.4 µg/L from 249 readings2019: median 1.4 µg/L from 267 readings2020: median 1.2 µg/L from 268 readings2021: median 1.2 µg/L from 258 readings2022: median 1.2 µg/L from 222 readings2023: median 1.2 µg/L from 346 readings2024: median 1.5 µg/L from 338 readings2025: median 1.1 µg/L from 277 readings2026: median 1.0 µg/L from 65 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 oligotrophic. That's common: clarity also depends on silt and colour, not just algae.

IndexClass
From secchi depth (2.1 m, 2015–2026)49mesotrophic
From total phosphorus (6.2 µg/L, 2015–2026)30oligotrophic
From chlorophyll a (1.2 µg/L, 2015–2026)32oligotrophic

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
20260.6 m (60)18 µg/L (78)1.0 µg/L (65)
20252.6 m (130)5.1 µg/L (424)1.1 µg/L (277)
20242.0 m (126)5.9 µg/L (464)1.5 µg/L (338)
20233.2 m (160)5.3 µg/L (449)1.2 µg/L (346)
20224.0 m (83)6.9 µg/L (311)1.2 µg/L (222)
20211.3 m (70)7.0 µg/L (259)1.2 µg/L (258)
20201.0 m (72)7.2 µg/L (250)1.2 µg/L (268)
20191.6 m (70)5.3 µg/L (239)1.4 µg/L (267)
20182.6 m (63)9.1 µg/L (251)1.4 µg/L (249)
20171.1 m (70)11 µg/L (164)0.5 µg/L (167)
20162.7 m (73)6.5 µg/L (202)0.9 µg/L (202)
20153.6 m (20)5.3 µg/L (190)1.0 µg/L (72)
2008–4.0 µg/L (9)–
19803.7 m (13)10 µg/L (15)1.2 µg/L (24)
19793.8 m (8)10 µg/L (13)1.3 µg/L (20)
19784.8 m (8)7.5 µg/L (10)1.2 µg/L (17)
19771.2 m (5)13 µg/L (7)2.8 µg/L (10)
19764.3 m (10)9.0 µg/L (11)1.5 µg/L (18)
19753.8 m (9)49 µg/L (9)4.4 µg/L (14)
19746.1 m (19)9.0 µg/L (11)–
19732.3 m (4)231 µg/L (6)–
19721.1 m (1)65 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

  • E300094 Upstream of Canada/us Border 1,152 readings
  • E300230 LK2 - Lake Koocanusa south of Elk River 1,111 readings
  • E300092 West of Grasmere 1,106 readings
  • E300093 Upstream of Gold Creek 1,097 readings
  • E300095 D/s Kikomun Creek 993 readings
  • E327373 RG_DSELK_R1 246 readings
  • E327374 RG_DSELK_R2 243 readings
  • E327372 RG_DSELK_L1 232 readings
  • E327371 RG_DSELK_L2 228 readings
  • 0200101 Koocanusa Lake off Elk River 133 readings
  • 0200169 Koocanusa Lake off Kikomun Creek 99 readings
  • E330332 Left Transect Lake Koocanusa U/s of Canada/us Border 84 readings
  • E330331 Far Left Transect Lake Koocanusa U/s of Canada/us Border 80 readings
  • E330337 Right Transect Valley Permit Receiving - Lake Koocanusa U/s of Gold Creek 80 readings
  • E330336 Left Transect Valley Permit Receiving - Lake Koocanusa U/s of Gold Creek 79 readings
  • E330335 Far Left Transect Valley Permit Receiving - Lake Koocanusa U/s of Gold Creek 78 readings
  • E330338 Far Right Transect Valley Permit Receiving - Lake Koocanusa U/s of Gold Creek 73 readings
  • E330333 Right Transect Lake Koocanusa U/s of Canada/us Border 67 readings
  • E330334 Far Right Transect Lake Koocanusa U/s of Canada/us Border 60 readings
  • 0200187 Koocanusa Lake south of Wardner 32 readings

And 3 more sites.

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.