PlaceDossier / BC places / Lakes

BC lake · 193 km² · Lower Arrow Lake watershed

Lower Arrow Lake

Its median summer total phosphorus over 2012–2026 was 3.6 µg/L, from 452 readings. Lower than 86% of the 100 BC lakes with enough recent readings (lower is clearer).

The readings

1,351 summer readings from open water on record from 1997 to 2026, at 5 sampling sites.

Median since 2012Compared with BC lakes
Total phosphorus3.6 µg/L
2012–2026, 452 readings		Lower than 86% of the 100 BC lakes with enough recent readings (lower is clearer).
Chlorophyll a2.1 µg/L
2019–2026, 155 readings		Higher than 54% 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 35 readings1998: median 3.0 µg/L from 31 readings1999: median 4.0 µg/L from 40 readings2000: median 5.0 µg/L from 41 readings2001: median 3.0 µg/L from 31 readings2002: median 3.0 µg/L from 22 readings2003: median 4.0 µg/L from 36 readings2004: median 3.0 µg/L from 41 readings2005: median 2.0 µg/L from 26 readings2006: median 3.0 µg/L from 26 readings2007: median 4.0 µg/L from 29 readings2008: median 4.0 µg/L from 28 readings2009: median 3.0 µg/L from 30 readings2010: median 3.0 µg/L from 27 readings2011: median 4.0 µg/L from 34 readings2012: median 3.3 µg/L from 33 readings2013: median 3.6 µg/L from 28 readings2014: median 2.5 µg/L from 32 readings2015: median 2.3 µg/L from 34 readings2016: median 2.9 µg/L from 34 readings2017: median 3.8 µg/L from 46 readings2018: median 4.8 µg/L from 33 readings2019: median 3.4 µg/L from 38 readings2020: median 4.1 µg/L from 27 readings2021: median 4.5 µg/L from 27 readings2022: median 3.8 µg/L from 36 readings2023: median 3.7 µg/L from 27 readings2024: median 3.6 µg/L from 27 readings2025: median 4.3 µg/L from 22 readings2026: median 3.5 µg/L from 8 readingsµg/L
Chlorophyll a the green pigment in algae: a direct measure of how much is growing
13 200020102020 1997: median 1.6 µg/L from 15 readings1998: median 1.1 µg/L from 15 readings1999: median 1.1 µg/L from 18 readings2000: median 1.1 µg/L from 24 readings2001: median 1.1 µg/L from 20 readings2002: median 3.0 µg/L from 15 readings2003: median 3.0 µg/L from 38 readings2004: median 3.4 µg/L from 44 readings2005: median 1.6 µg/L from 23 readings2006: median 1.5 µg/L from 28 readings2007: median 2.3 µg/L from 27 readings2019: median 2.4 µg/L from 15 readings2020: median 3.0 µg/L from 18 readings2021: median 2.5 µg/L from 23 readings2022: median 2.2 µg/L from 29 readings2023: median 1.7 µg/L from 21 readings2024: median 1.6 µg/L from 23 readings2025: median 1.5 µg/L from 19 readings2026: median 2.1 µg/L from 7 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 (3.6 µg/L, 2012–2026)23oligotrophic
From chlorophyll a (2.1 µg/L, 2019–2026)38oligotrophic

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
20263.5 µg/L (8)2.1 µg/L (7)
20254.3 µg/L (22)1.5 µg/L (19)
20243.6 µg/L (27)1.6 µg/L (23)
20233.7 µg/L (27)1.7 µg/L (21)
20223.8 µg/L (36)2.2 µg/L (29)
20214.5 µg/L (27)2.5 µg/L (23)
20204.1 µg/L (27)3.0 µg/L (18)
20193.4 µg/L (38)2.4 µg/L (15)
20184.8 µg/L (33)–
20173.8 µg/L (46)–
20162.9 µg/L (34)–
20152.3 µg/L (34)–
20142.5 µg/L (32)–
20133.6 µg/L (28)–
20123.3 µg/L (33)–
20114.0 µg/L (34)–
20103.0 µg/L (27)–
20093.0 µg/L (30)–
20084.0 µg/L (28)–
20074.0 µg/L (29)2.3 µg/L (27)
20063.0 µg/L (26)1.5 µg/L (28)
20052.0 µg/L (26)1.6 µg/L (23)
20043.0 µg/L (41)3.4 µg/L (44)
20034.0 µg/L (36)3.0 µg/L (38)
20023.0 µg/L (22)3.0 µg/L (15)
20013.0 µg/L (31)1.1 µg/L (20)
20005.0 µg/L (41)1.1 µg/L (24)
19994.0 µg/L (40)1.1 µg/L (18)
19983.0 µg/L (31)1.1 µg/L (15)
19975.0 µg/L (35)1.6 µg/L (15)

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

  • E225782 Arrow Lake at Bowman Creek (AR7) 648 readings
  • E225783 Arrow Lake at Cayuse Creek (AR8) 384 readings
  • E225781 Arrow Lake at Johnson Creek (AR6) 317 readings
  • 0200524 Arrow Lake opposite Syringa Creek 1 reading
  • E249075 U/s Hugh Keenleyside Dam (Eem Iii: CGBD2) 1 reading

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.