St. Louis city County Lake Quality
Missouri, 5 lakes, average grade D (Nutrient-rich)
St. Louis city County has 5 monitored 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. 3 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county-wide average grade is D — water quality issues are persistent across most of the monitored basins. 0 lakes fall into the F bracket outright.
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. Boathouse Lake (D) is the cleanest in the county.
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Quick Answers for St. Louis city County
Planning a trip? Check special fishing regulations for Boathouse Lake — or check the official Missouri fishing regulations.
All Lakes in St. Louis city County
5 lakes · 3 graded, 2 not rated3 graded lakes · 2 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | DBoathouse LakeSt. Louis city | D | 2.3 ft | 59.8 µg/L | 18 µg/L | No recent samples | Not recorded |
| 2 | DLafayette Park LakeSt. Louis city | D | 2.3 ft | 127.5 µg/L | 18.2 µg/L | No recent samples | Not recorded |
| 3 | DForest Park PondSt. Louis city | D | 1.6 ft | 68.8 µg/L | 23.3 µg/L | No recent samples | Not recorded |
| NRO'Fallon Park LakeSt. Louis city | NR | 1.6 ft | 335 µg/L | 2 µg/L | No recent samples | Not recorded | |
| NRJefferson LakeSt. Louis city | NR | No recent samples | 70 µg/L | 55.2 µg/L | No recent samples | Not recorded |
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 Missouri
See how St. Louis city 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.