Harrison County Lake Quality
Ohio, 3 lakes — no lake here has enough monitoring data for a grade
Harrison County has 3 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. No lake in Harrison County has enough sampling behind it for an A–F grade yet. The 3 monitored lakes below carry whatever clarity, phosphorus, and chlorophyll-a measurements exist.
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.
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Quick Answers for Harrison County
Planning a trip? Check special fishing regulations for Tapan Lake Adj To Marina — or check the official Ohio fishing regulations.
All Lakes in Harrison County
3 lakes · 0 graded, 3 not rated0 graded lakes · 3 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRTapan Lake Adj To MarinaHarrison | NR | No recent samples | 47.1 µg/L | 65.3 µg/L | No recent samples | ✓ Public | |
| NRTappan Lake @ Cadiz Public Water Supply IntakeHarrison | NR | No recent samples | 66.1 µg/L | 72.1 µg/L | No recent samples | Not recorded | |
| NRClendening LakeHarrison | 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 Ohio
See how Harrison 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.