Morton County Lake Quality
North Dakota, 7 lakes, average grade F (Algae-prone)
Morton County holds 7 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 4 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county average is F — the most-stressed bracket in our rubric. Most monitored lakes here show persistent nutrient loading and algal pressure.
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 Nygren Dam Lake (D); the most-stressed is Sweetbriar Dam Lake (F).
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Quick Answers for Morton County
Planning a trip? Check special fishing regulations for Nygren Dam Lake — or check the official North Dakota fishing regulations.
All Lakes in Morton County
7 lakes · 4 graded, 3 not rated4 graded lakes · 3 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | DNygren Dam LakeMorton | D | 2.6 ft | 73 µg/L | 24.7 µg/L | No recent samples | ✓ Public |
| 2 | FSweetbriar Dam LakeMorton | F | 3 ft | 353 µg/L | 54 µg/L | No recent samples | ✓ Public |
| 3 | FSweet Briar Dam-Mid ReservoirMorton | F | 3 ft | 239.5 µg/L | 36.9 µg/L | No recent samples | ✓ Public |
| 4 | FHarmon LakeMorton | F | No recent samples | 20 µg/L | 48.5 µg/L | No recent samples | ✓ Public |
| NRFish Creek LakeMorton | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRStorm Creek LakeMorton | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRCrown Butte LakeMorton | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public |
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 Morton 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.