Lennox and Addington County Lake Quality
Ontario, 18 lakes, average grade A (Excellent)
Lennox and Addington County's 18 graded lakes fall in the moderate-density bracket for Ontario. The county-level average smooths over real differences — a single agricultural watershed near the southwest corner can pull the average down even if the rest of the county runs clean. On average, Lennox and Addington County lakes grade an A. That puts it near the top of the Ontario county ranking.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Ashby Lake (A) is the cleanest in the county.
Quick Answers for Lennox and Addington County
Planning a trip? Check special fishing regulations for Ashby Lake — or check the official Ontario fishing regulations.
All Lakes in Lennox and Addington County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Ashby Lake | A | 18 ft | - |
| 2 | Sheldrake Lake | A | - | 16.3 µg/L |
| 3 | Cade Lake | A | - | 18.8 µg/L |
| 4 | Browns Lake | A | - | 9.3 µg/L |
| 5 | Long Mallory Lake | A | - | 6.7 µg/L |
| 6 | Mocassin Lake | A | - | 8.8 µg/L |
| 7 | Trout Lake | A | - | 9.3 µg/L |
| 8 | Crystal Lake | A | 18 ft | 6.5 µg/L |
| 9 | Leatherroot Lake | A | 23 ft | 5.2 µg/L |
| 10 | Beaver Lake | A | 12.8 ft | 14.9 µg/L |
| 11 | Skootamatta Lake | A | 13.5 ft | 9.3 µg/L |
| 12 | Weslemkoon Lake | A | 14.1 ft | 6.8 µg/L |
| 13 | Otter Lake | A | 10.8 ft | 6.8 µg/L |
| 14 | Joeperry Lake | A | 10.8 ft | 6.5 µg/L |
| 15 | Pringle Lake | B | 7.9 ft | 10.1 µg/L |
| 16 | Sheffield Long Lake | B | 8.5 ft | 11.5 µg/L |
| 17 | Gull Lake | B | 9.8 ft | 9.3 µg/L |
| 18 | Effingham Lake | B | 6.2 ft | 9.5 µg/L |
Other Counties in Ontario
See how Lennox and Addington County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 38 states.
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Source: EPA National Aquatic Resource Surveys, 2026.