Mercer County Lake Quality
North Dakota, 5 lakes, average grade B (Good)
Mercer County has 5 graded 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. With an average grade of B, Mercer County sits comfortably above the North Dakota median.
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. Qacmainstfbk Lake (A) is the cleanest in the county.
Quick Answers for Mercer County
Planning a trip? Check special fishing regulations for Qacmainstfbk Lake, whether the fish are safe to eat, and the best times to fish — or check the official North Dakota fishing regulations.
Fishing in Mercer County
All Lakes in Mercer County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Qacmainstfbk Lake | A | - | - | 10 µg/L |
| 2 | Qacmainstdup Lake | B | - | - | 10 µg/L |
| 3 | Harmony Lake | C | 2.3 ft | 21.2 ft | - |
Other Counties in North Dakota
See how Mercer County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 15 states.
Where to stay near Mercer County
Top-rated places to stay near Mercer County
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Source: EPA National Aquatic Resource Surveys, 2026.