St John Lake
Simcoe, OntarioView mapDirections
Ontario MECP publishes the water-quality measurements for St John Lake. Here is what has been measured.
- 45 ft max depth
St John Lake in Simcoe, Ontario has water-quality measurements published by Ontario MECP, shown here as reported. Water clarity: 2.5 m visibility. Phosphorus: 29.4 µg/L.
St John Lake is a lake in Simcoe County, Ontario with an estimated average depth of about 45 feet.
Source: Ontario open-data programmes (Lake Partner Program and Broad-scale Monitoring) — not the EPA Water Quality Portal, last sampled 2025-10-13. Methodology: how these readings are compared.
Swimming conditions
No readingNot rated
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether St John Lake is safe to swim in today is a call for the Ontario Ministry of the Environment, Conservation and Parks and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for St John Lake
These are the measurements Ontario MECP publishes for St John Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 8.2 ft. Phosphorus 29.4 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 2.5m | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 29.4µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
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Lake Details
Max depth
~13.7 m est.
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Ontario has not published bathymetry for St John Lake.
Lake Size & Watershed
Watershed (drainage) area
21 sq mi
HydroLAKES / HydroSHEDS
Surface area
1,616 acres
HydroLAKES / HydroSHEDS
Shoreline
10 mi
HydroLAKES / HydroSHEDS
Elevation
702 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
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Frequently asked questions about St John Lake
Where is St John Lake?
- St John Lake is a lake in Simcoe, Ontario. Its water-quality measurements are published by Ontario MECP and shown on this page as reported.
What is the water quality of St John Lake?
- St John Lake in Simcoe, Ontario has water-quality measurements published by Ontario MECP, shown here as reported. Water clarity: 2.5 m visibility. Phosphorus: 29.4 µg/L.
Is St John Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is St John Lake?
- No published bathymetric survey covers St John Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 45 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
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Where this data comes from
Measurements for St John Lake come from Ontario open-data programmes (Lake Partner Program and Broad-scale Monitoring), not the EPA Water Quality Portal. Per-sample source details are not recorded for this lake. Contains information licensed under the Open Government Licence – Ontario. See data sources.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)