Northumberland County, Ontario · Water Quality Report Card
Lake Seymour
Lake Seymour in Northumberland, Ontario received a water quality grade of C (Fair). Water clarity: 1.7 m visibility. Phosphorus: 22.8 µg/L.
- Clarity
- 1.7 m
- Type
- Eutrophic
Lake Seymour is a productive, nutrient-rich eutrophic lake in Northumberland County, Ontario. Water quality is graded C based on 2 sampling years through 2025. Compared to the 2 other monitored lakes in Northumberland County, Lake Seymour ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Ontario MECP, last sampled 2025-09-10. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 5.6 ft. Phosphorus level: 22.8 µg/L. Trophic State Index: 51.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.7 m | D |
| Phosphorus | 22.8 µg/L | B |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lake Seymour
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Fishing Lake Seymour
Location
County Ranking
Ranked #2 of 3 lakes in Northumberland
Cleaner Lakes Within 30 Miles
Lake Seymour holds Grade C. 5 nearby lakes hold higher grades.
- ABelmont LakePeterborough · 8.7 mi · Two grade letters higher (C → A)
- AOak LakePeterborough · 15.2 mi · Two grade letters higher (C → A)
- ARound LakePeterborough · 8 mi · Two grade letters higher (C → A)
- ARylstone LakeHastings · 8.2 mi · Two grade letters higher (C → A)
- ACrowe LakeHastings · 9.9 mi · Two grade letters higher (C → A)
Nearby Lakes in Northumberland
Explore Lake Seymour across LakeGrade
More Ontario Lake Rankings
Other Grade C Lakes in Ontario
Eutrophic Lakes in Ontario
More records, surveys & data sources
Where this data comes from
Measurements for Lake Seymour 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: 2025-09-10
Monitoring stations: