PlaceDossier / BC places / Lakes
BC lake · 1 km² · Lillooet watershed
Alta Lake
Its median summer Secchi depth over 2015–2025 was 6.4 m, from 45 readings. Clearer than 72% of the 62 BC lakes with enough recent readings.
The readings
163 summer readings from open water on record from 2009 to 2025, at 1 sampling site.
| Median since 2012 | Compared with BC lakes | |
|---|---|---|
| Secchi depth | 6.4 m 2015–2025, 45 readings | Clearer than 72% of the 62 BC lakes with enough recent readings. |
| Total phosphorus | 3.5 µg/L 2015–2025, 55 readings | Lower than 88% of the 100 BC lakes with enough recent readings (lower is clearer). |
| Chlorophyll a | 1.0 µg/L 2015–2025, 45 readings | Lower than 82% of the 83 BC lakes with enough recent 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, 2015–2025) | 33 | oligotrophic |
| From total phosphorus (3.5 µg/L, 2015–2025) | 22 | oligotrophic |
| From chlorophyll a (1.0 µg/L, 2015–2025) | 31 | oligotrophic |
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
| Year | Secchi depth | Total phosphorus | Chlorophyll a |
|---|---|---|---|
| 2025 | 6.8 m (11) | 3.5 µg/L (17) | 1.0 µg/L (11) |
| 2024 | 7.1 m (11) | 3.7 µg/L (14) | 0.6 µg/L (11) |
| 2023 | 6.3 m (13) | 4.2 µg/L (14) | 1.0 µg/L (13) |
| 2022 | 7.0 m (1) | 3.3 µg/L (1) | 0.9 µg/L (1) |
| 2021 | 6.6 m (1) | 3.1 µg/L (1) | 1.6 µg/L (1) |
| 2020 | 5.2 m (1) | 3.9 µg/L (1) | 1.6 µg/L (1) |
| 2019 | 5.1 m (2) | 3.9 µg/L (2) | 2.9 µg/L (2) |
| 2018 | 4.0 m (1) | 5.9 µg/L (1) | 1.5 µg/L (1) |
| 2017 | 5.4 m (2) | 3.1 µg/L (2) | 0.8 µg/L (2) |
| 2016 | 6.0 m (1) | 2.3 µg/L (1) | 1.0 µg/L (1) |
| 2015 | 6.5 m (1) | 2.4 µg/L (1) | 1.1 µg/L (1) |
| 2011 | – | 3.0 µg/L (4) | 0.6 µg/L (3) |
| 2010 | – | 3.5 µg/L (4) | 0.9 µg/L (2) |
| 2009 | – | 3.0 µg/L (3) | 0.9 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
- E275784 North deep site 163 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.