Seneca County Lake Quality
New York, 4 lakes, average grade A (Excellent)
Seneca County has 4 monitored lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. 1 of those lake carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county's average grade is A — among the cleanest in New York. 1 lakes pull an A on their own, and almost none fall into the D or F brackets.
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. Seneca Lake Platform (A) is the cleanest in the county.
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Quick Answers for Seneca County
Planning a trip? Check special fishing regulations for Seneca Lake Platform — or check the official New York fishing regulations.
All Lakes in Seneca County
4 lakes · 1 graded, 3 not rated1 graded lake · 3 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | ASeneca Lake PlatformSeneca | A | 11.5 ft | 8 µg/L | 2.8 µg/L | No recent samples | ✓ Public |
| NRGem LakeSeneca | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRBlack LakeSeneca | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRVan Cleef LakeSeneca | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded |
NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
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Other Counties in New York
See how Seneca County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.