Parry Sound District County, Ontario · Water Quality Report Card
Mason Lake
Mason Lake in Parry Sound District, Ontario received a water quality grade of A (Excellent). Water clarity: 3.2 m visibility. Phosphorus: 5.4 µg/L.
- Clarity
- 3.2 m
- Type
- Oligotrophic
Mason Lake is a cold, clear oligotrophic lake in Parry Sound District County, Ontario. Water quality is graded A based on 2 sampling years through 2025. Compared to the 230 other monitored lakes in Parry Sound District County, Mason Lake ranks #106 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
Good clarity, visible to about 10.5 ft. Phosphorus level: 5.4 µg/L. Trophic State Index: 36.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.2 m | B |
| Phosphorus | 5.4 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
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Fishing Mason Lake
Location
County Ranking
Ranked #106 of 231 lakes in Parry Sound District
Nearby Lakes in Parry Sound District
Explore Mason 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 Mason 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: