Durham Region County, Ontario · Water Quality Report Card
Chalk Lake
Chalk Lake in Durham Region, Ontario received a water quality grade of A (Excellent). Water clarity: 4.6 m visibility. Phosphorus: 8.4 µg/L.
- Clarity
- 4.6 m
- Type
- Oligotrophic
Chalk Lake is a cold, clear oligotrophic lake in Durham Region County, Ontario. Water quality is graded A based on 2 sampling years through 2025. Compared to the 1 other monitored lakes in Durham Region County, Chalk Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Ontario MECP, last sampled 2025-09-29. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 14.9 ft down. Phosphorus level: 8.4 µg/L. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.55 m | A |
| Phosphorus | 8.4 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 37 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
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Fishing Chalk Lake
Location
County Ranking
Ranked #1 of 2 lakes in Durham Region
Nearby Lakes in Durham Region
Explore Chalk Lake across LakeGrade
More Ontario Lake Rankings
Other Grade A Lakes in Ontario
Oligotrophic Lakes in Ontario
More records, surveys & data sources
Where this data comes from
Measurements for Chalk Lake come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.
Data Sources
Water quality data from the EPA Water Quality Portal
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Most recent sample: 2025-09-29
Monitoring stations: