BC lake · 26.8 ha · Columbia River watershed

Lillian Lake

Its median summer total phosphorus over 2024–2026 was 6.3 µg/L, from 45 readings. Lower than 59% of the 95 BC lakes with enough recent readings (lower is clearer).

The readings

95 summer readings from open water on record from 2024 to 2026, at 1 sampling site.

	Median since 2012	Compared with BC lakes
Secchi depth	Too few readings to judge 21 readings since 2012, in 2 years	Too few readings to compare (21 readings since 2012, in 2 years).
Total phosphorus	6.3 µg/L 2024–2026, 45 readings	Lower than 59% of the 95 BC lakes with enough recent readings (lower is clearer).
Chlorophyll a	1.1 µg/L 2024–2026, 29 readings	Lower than 76% 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

Total phosphorus the nutrient that most often feeds algae in BC lakes

Chlorophyll a the green pigment in algae: a direct measure of how much is growing

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 total phosphorus (6.3 µg/L, 2024–2026)	31	oligotrophic
From chlorophyll a (1.1 µg/L, 2024–2026)	32	oligotrophic

Left out for too few recent readings (we need at least 10 summer readings from open water, spread over at least 3 different years, since 2012): secchi depth (21 readings since 2012, in 2 years).

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
2026	–	6.0 µg/L (10)	0.8 µg/L (8)
2025	5.3 m (10)	6.7 µg/L (24)	1.1 µg/L (10)
2024	5.3 m (11)	6.0 µg/L (11)	1.6 µg/L (11)

Median of each year's May to October readings; the number of readings is in brackets.

Where it was sampled

0200435 Main basin 95 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 the water receiving its discharge, 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.