Oliver County Lake Quality
North Dakota, 4 lakes, average grade C (Fair)
Oliver County holds 4 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 3 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. Oliver County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.
The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is East Arroda Lake (C); the most-stressed is East Arroda Lake (C).
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Quick Answers for Oliver County
Planning a trip? Check special fishing regulations for East Arroda Lake — or check the official North Dakota fishing regulations.
All Lakes in Oliver County
4 lakes · 3 graded, 1 not rated3 graded lakes · 1 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | CEast Arroda LakeOliver | C | 5.6 ft | 56 µg/L | 6.2 µg/L | No recent samples | ✓ Public |
| 2 | CNelson LakeOliver | C | 1.3 ft | 275 µg/L | 23.1 µg/L | No recent samples | ✓ Public |
| 3 | CArroda LakeOliver | C | 6.7 ft | 26.5 µg/L | 3 µg/L | No recent samples | Not recorded |
| NRMandan LakeOliver | 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 North Dakota
See how Oliver 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.