BC lake · 2 km² · South Thompson River watershed

Roche Lake

Its median summer Secchi depth over 2015–2018 was 3.7 m, from 8 readings. Murkier than 71% of the 122 BC lakes with at least 5 readings.

The readings

38 summer readings on record from 1991 to 2018, at 2 sampling sites.

	Median, latest 10 sampled years	Compared with BC lakes
Secchi depth	3.7 m 2015–2018, 8 readings	Murkier than 71% of the 122 BC lakes with at least 5 readings.
Total phosphorus	24 µg/L 2014–2018, 11 readings	Higher than 75% of the 269 BC lakes with at least 5 readings.
Chlorophyll a	6.1 µg/L 2014–2018, 9 readings	Higher than 83% 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: clarity reads mesotrophic, phosphorus reads eutrophic, algae reads mesotrophic. That's common: clarity also depends on silt and colour, not just algae.

	Index	Class
From secchi depth (3.7 m, 2015–2018)	41	mesotrophic
From total phosphorus (24 µg/L, 2014–2018)	50	eutrophic
From chlorophyll a (6.1 µg/L, 2014–2018)	48	mesotrophic

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
2018	2.5 m (1)	40 µg/L (1)	2.2 µg/L (1)
2017	2.9 m (2)	23 µg/L (2)	20 µg/L (2)
2016	3.7 m (4)	19 µg/L (4)	5.5 µg/L (4)
2015	4.7 m (1)	26 µg/L (3)	6.5 µg/L (1)
2014	–	21 µg/L (1)	5.6 µg/L (1)
2003	–	156 µg/L (4)	–
1999	–	53 µg/L (2)	–
1993	–	14 µg/L (2)	–
1991	–	15 µg/L (2)	–

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

Where it was sampled

E206789 ROCHE LAKE AT CENTRE 46 readings
E216177 ROCHE LAKE NEAR RESORT 1 reading

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.