Morton County Lake Quality
Wisconsin, 4 lakes, average grade F (Very Poor)
Only 4 lakes in Morton County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. 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).
Quick Answers for Morton County
Planning a trip? Check special fishing regulations for Nygren Dam Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Morton County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Nygren Dam Lake | D | 2.6 ft | - | - |
| 2 | Sweetbriar Dam Lake | F | 3 ft | - | - |
| 3 | Sweet Briar Dam-Mid Reservoir | F | 3 ft | - | - |
| 4 | Harmon Lake | F | - | - | - |
Source: EPA National Aquatic Resource Surveys, 2026.