PlaceDossier / BC places / Lakes
BC lake · 254 km² · Francois Lake watershed
François Lake
Its median summer Secchi depth over 2016–2025 was 6.4 m, from 47 readings. Clearer than 70% of the 122 BC lakes with at least 5 readings.
The readings
220 summer readings on record from 1998 to 2025, at 6 sampling sites.
| Median, latest 10 sampled years | Compared with BC lakes | |
|---|---|---|
| Secchi depth | 6.4 m 2016–2025, 47 readings | Clearer than 70% of the 122 BC lakes with at least 5 readings. |
| Total phosphorus | 6.5 µg/L 2016–2025, 107 readings | Lower than 67% of the 269 BC lakes with at least 5 readings (lower is clearer). |
| Chlorophyll a | 1.5 µg/L 2016–2025, 46 readings | Lower than 59% of the 156 BC lakes with at least 5 readings (lower is clearer). |
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).
| Index | Class | |
|---|---|---|
| From secchi depth (6.4 m, 2016–2025) | 33 | oligotrophic |
| From total phosphorus (6.5 µg/L, 2016–2025) | 31 | oligotrophic |
| From chlorophyll a (1.5 µg/L, 2016–2025) | 34 | oligotrophic |
Inferred by us, not a provincial classification. 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. 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.
Year by year
| Year | Secchi depth | Total phosphorus | Chlorophyll a |
|---|---|---|---|
| 2025 | 8.3 m (4) | 6.3 µg/L (14) | 1.7 µg/L (4) |
| 2024 | 6.8 m (4) | 45 µg/L (26) | 1.2 µg/L (4) |
| 2023 | 6.8 m (4) | 25 µg/L (26) | 1.0 µg/L (4) |
| 2022 | 6.0 m (4) | 7.9 µg/L (10) | 1.6 µg/L (3) |
| 2021 | 5.7 m (6) | 4.9 µg/L (6) | 1.1 µg/L (6) |
| 2020 | 4.8 m (1) | 3.1 µg/L (1) | 1.6 µg/L (1) |
| 2019 | 5.9 m (6) | 4.9 µg/L (6) | 1.6 µg/L (6) |
| 2018 | 5.8 m (6) | 5.4 µg/L (6) | 1.5 µg/L (6) |
| 2017 | 6.7 m (6) | 4.8 µg/L (6) | 1.5 µg/L (6) |
| 2016 | 6.2 m (6) | 4.4 µg/L (6) | 2.7 µg/L (6) |
| 2015 | – | 3.1 µg/L (4) | 3.6 µg/L (3) |
| 2008 | – | 5.0 µg/L (5) | – |
| 1999 | – | 53 µg/L (4) | – |
| 1998 | – | 53 µg/L (4) | – |
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
- E319892 CONTROL - FRANCOIS LAKE 118 readings
- E224946 FRANCOIS LAKE EAST END DEEP STATION 65 readings
- E271703 FRANCOIS LAKE CENTRE DEEP STATION 57 readings
- E224945 FRANCOIS LAKE WEST END DEEP STATION 42 readings
- E319894 FLC-2 FRANCOIS LAKE 100 M DOWNSTREAM OF LOWER SWEETNAM CK 10 readings
- E319893 FLC-1 FRANCOIS LAKE 100 M DOWNSTREAM OF SOUTH UNNAMED CREEK 10 readings
Site names and IDs are as recorded in the provincial database; 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. Each year's figure is the median of that year's readings; the summary is the median of every reading in the lake's latest 10 sampled years. 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.