O'Fallon Park Lake is a productive, nutrient-rich eutrophic lake in St. Louis city County, Missouri. Water quality is graded D based on 3 sampling years through 2021. Compared to the 4 other monitored lakes in St. Louis city County, O'Fallon Park Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2021-07-17. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 1.6 ft of visibility. Phosphorus level: 335 µg/L. Chlorophyll-a: 2 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | 335 µg/L | F |
| Chlorophyll-a (Algae) | 2 µg/L | A |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near O'Fallon Park Lake
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Fishing O'Fallon Park Lake
Location
County Ranking
Ranked #2 of 5 lakes in St. Louis city County
Nearby Lakes in St. Louis city County
Explore O'Fallon Park Lake across LakeGrade
More Missouri Lake Rankings
Other Grade D Lakes in Missouri
St. Louis County · Clarity: 1.8 ft
St. Louis County · Clarity: 2.5 ft
St. Charles County · Clarity: 2.7 ft
St. Charles County · Clarity: 3.2 ft
St. Charles County · Clarity: 2.6 ft
Franklin County · Clarity: 2.6 ft
Eutrophic Lakes in Missouri
More records, surveys & data sources
Regulated Pollution Sources Nearby
14 EPA-permitted facilities operate within about 5 miles of O'Fallon Park Lake under Clean Water Act (NPDES) discharge permits, including 2 classified by the EPA as major dischargers. 5 facilities have a reported Clean Water Act violation in the past three years.
- Msd Bissell Point WwtpSt Louis · 1.5 mi away · NPDES MO0025178MajorRecent violation
- Illinois American Water Company - Granite City WwtpGranite City · 2.3 mi away · NPDES IL0033481MajorRecent violation
- Illinois Department Of TransportationVenice · 2.2 mi away · NPDES IL0071765Recent violation
- Municipal River TerminalSt. Louis · 2.5 mi away · NPDES MO0113328Recent violation
- Venice Energy CenterVenice · 3 mi away · NPDES IL0000175Recent violation
- Stericycle St LouisSt. Louis · 0.7 mi away · NPDES MONX00148
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2021-07-17
Monitoring stations: 1