PlaceDossier / BC places / Lakes

BC lake · 319 km² · Upper Arrow Lake watershed

Upper Arrow Lake

Its median summer total phosphorus over 2012–2026 was 4.2 µg/L, from 491 readings. Lower than 79% of the 100 BC lakes with enough recent readings (lower is clearer).

The readings

1,681 summer readings from open water on record from 1997 to 2026, at 6 sampling sites.

Median since 2012Compared with BC lakes
Total phosphorus4.2 µg/L
2012–2026, 491 readings		Lower than 79% of the 100 BC lakes with enough recent readings (lower is clearer).
Chlorophyll a2.6 µg/L
2019–2026, 180 readings		Higher than 61% of the 83 BC lakes with enough recent readings.
Total phosphorus the nutrient that most often feeds algae in BC lakes
310 200020102020 1997: median 5.0 µg/L from 41 readings1998: median 3.0 µg/L from 35 readings1999: median 5.0 µg/L from 66 readings2000: median 5.0 µg/L from 59 readings2001: median 4.0 µg/L from 47 readings2002: median 2.5 µg/L from 34 readings2003: median 4.0 µg/L from 54 readings2004: median 3.5 µg/L from 54 readings2005: median 3.0 µg/L from 33 readings2006: median 3.0 µg/L from 41 readings2007: median 3.0 µg/L from 43 readings2008: median 3.5 µg/L from 30 readings2009: median 3.0 µg/L from 27 readings2010: median 3.0 µg/L from 25 readings2011: median 4.0 µg/L from 30 readings2012: median 3.1 µg/L from 29 readings2013: median 4.4 µg/L from 33 readings2014: median 3.5 µg/L from 39 readings2015: median 2.7 µg/L from 46 readings2016: median 3.4 µg/L from 39 readings2017: median 3.1 µg/L from 41 readings2018: median 5.4 µg/L from 36 readings2019: median 4.2 µg/L from 35 readings2020: median 4.8 µg/L from 30 readings2021: median 4.6 µg/L from 31 readings2022: median 4.3 µg/L from 38 readings2023: median 4.9 µg/L from 30 readings2024: median 4.8 µg/L from 24 readings2025: median 5.0 µg/L from 26 readings2026: median 3.8 µg/L from 14 readingsµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
13 200020102020 1997: median 2.0 µg/L from 20 readings1998: median 1.1 µg/L from 19 readings1999: median 1.1 µg/L from 30 readings2000: median 1.2 µg/L from 36 readings2001: median 1.1 µg/L from 32 readings2002: median 2.5 µg/L from 22 readings2003: median 3.1 µg/L from 54 readings2004: median 3.4 µg/L from 63 readings2005: median 2.5 µg/L from 33 readings2006: median 1.8 µg/L from 42 readings2007: median 2.0 µg/L from 40 readings2019: median 3.0 µg/L from 17 readings2020: median 3.0 µg/L from 23 readings2021: median 3.1 µg/L from 25 readings2022: median 2.6 µg/L from 42 readings2023: median 2.2 µg/L from 22 readings2024: median 2.7 µg/L from 23 readings2025: median 2.1 µg/L from 22 readings2026: median 3.4 µg/L from 6 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 (4.2 µg/L, 2012–2026)25oligotrophic
From chlorophyll a (2.6 µg/L, 2019–2026)40oligotrophic

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

YearTotal phosphorusChlorophyll a
20263.8 µg/L (14)3.4 µg/L (6)
20255.0 µg/L (26)2.1 µg/L (22)
20244.8 µg/L (24)2.7 µg/L (23)
20234.9 µg/L (30)2.2 µg/L (22)
20224.3 µg/L (38)2.6 µg/L (42)
20214.6 µg/L (31)3.1 µg/L (25)
20204.8 µg/L (30)3.0 µg/L (23)
20194.2 µg/L (35)3.0 µg/L (17)
20185.4 µg/L (36)–
20173.1 µg/L (41)–
20163.4 µg/L (39)–
20152.7 µg/L (46)–
20143.5 µg/L (39)–
20134.4 µg/L (33)–
20123.1 µg/L (29)–
20114.0 µg/L (30)–
20103.0 µg/L (25)–
20093.0 µg/L (27)–
20083.5 µg/L (30)–
20073.0 µg/L (43)2.0 µg/L (40)
20063.0 µg/L (41)1.8 µg/L (42)
20053.0 µg/L (33)2.5 µg/L (33)
20043.5 µg/L (54)3.4 µg/L (63)
20034.0 µg/L (54)3.1 µg/L (54)
20022.5 µg/L (34)2.5 µg/L (22)
20014.0 µg/L (47)1.1 µg/L (32)
20005.0 µg/L (59)1.2 µg/L (36)
19995.0 µg/L (66)1.1 µg/L (30)
19983.0 µg/L (35)1.1 µg/L (19)
19975.0 µg/L (41)2.0 µg/L (20)

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

  • E225769 Arrow Lake at Ann Point (AR2) 646 readings
  • E225770 Arrow Lake at Turner Creek (AR3) 373 readings
  • E225768 Arrow Lake at Albert Point (AR1) 318 readings
  • E225771 Arrow Lake at Slewiskin Creek (AR4) 178 readings
  • E225779 Arrow Lake D/s Mosquito Creek (AR5) 148 readings
  • E305210 Arrow Lake, Beaton arm (HL1) 18 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.