St. Louis County Lake Quality
Wisconsin, 9 lakes, average grade F (Very Poor)
Only 9 lakes in St. Louis 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 Simpson Park Lake (D); the most-stressed is Creve Coeur Lake (F).
Quick Answers for St. Louis County
Planning a trip? Check special fishing regulations for Simpson Park Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in St. Louis County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Simpson Park Lake | D | 1.8 ft | - | 73 µg/L |
| 2 | Simpson Park Lake | D | 2.5 ft | - | 36 µg/L |
| 3 | Mallard Lake | F | 1.9 ft | - | 84 µg/L |
| 4 | Creve Coeur Lake | F | 1.6 ft | - | 101 µg/L |
| 5 | Koeneman Park Lake | F | 3.1 ft | - | 270.8 µg/L |
| 6 | Spanish Lake | F | 1.6 ft | - | 347.8 µg/L |
| 7 | Creve Coeur Lake Nr. Boat Ramp | F | 1.2 ft | - | 100 µg/L |
| 8 | Bee Tree Lake | F | 0.6 ft | - | 263 µg/L |
| 9 | Tilles Park Reservoir | F | - | - | 434.5 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.