BC lake · 2 km² · Lower North Thompson River watershed

Birch Lake

Its median summer Secchi depth over 2012–2017 was 4.4 m, from 3 readings.

The readings

13 summer readings on record from 2012 to 2017, at 1 sampling site.

	Median, latest 10 sampled years	Compared with BC lakes
Secchi depth	4.4 m 2012–2017, 3 readings	Too few readings (3) to compare with other lakes.
Total phosphorus	13 µg/L 2012–2017, 5 readings	Higher than 55% of the 269 BC lakes with at least 5 readings.
Chlorophyll a	2.4 µg/L 2012–2017, 5 readings	Higher than 58% of the 156 BC lakes with at least 5 readings.

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

The measures disagree: phosphorus reads mesotrophic, algae reads oligotrophic. That's common: clarity also depends on silt and colour, not just algae.

	Index	Class
From total phosphorus (13 µg/L, 2012–2017)	41	mesotrophic
From chlorophyll a (2.4 µg/L, 2012–2017)	39	oligotrophic

Left out for too few readings (under 5 in the latest 10 sampled years): secchi depth.

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
2017	5.0 m (2)	8.2 µg/L (2)	2.2 µg/L (2)
2014	–	18 µg/L (1)	4.1 µg/L (1)
2013	–	11 µg/L (1)	2.3 µg/L (1)
2012	4.3 m (1)	17 µg/L (1)	2.4 µg/L (1)

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

Where it was sampled

E289729 BIRCH LAKE @ DEEPEST POINT 13 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.