Mercer County Lake Quality
North Dakota, 1 lake, average grade C (Fair)
Mercer County has 1 monitored lake — 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. Every one of those lake carries an A–F grade, so the county-level summary covers the full set rather than a monitored subset. The county average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
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 Harmony Lake (C); the most-stressed is Harmony Lake (C).
Where to stay near Mercer County
Top-rated places to stay near Mercer County
Prices for Sep 11–13, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip to Mercer County?
Get lake water-quality report cards plus the best cabin & lodging deals near Mercer County — straight to your inbox. No spam, unsubscribe anytime.
Quick Answers for Mercer County
Planning a trip? Check special fishing regulations for Harmony Lake — or check the official North Dakota fishing regulations.
All Lakes in Mercer County
1 lake1 graded lake
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | CHarmony LakeMercer | C | 2.3 ft | 67.5 µg/L | 8.4 µg/L | No recent samples | ✓ Public |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
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 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.