Jefferson Lake is a productive, nutrient-rich eutrophic lake in St. Louis city County, Missouri. Water quality is graded D based on 2 sampling years through 2020. Overall water quality is improving over recent sampling years. Compared to the 4 other monitored lakes in St. Louis city County, Jefferson Lake ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2020-08-24. 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
No clarity data. Phosphorus level: 70 µg/L. Chlorophyll-a: 55.2 µg/L. Trophic State Index: 68.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 70 µg/L | D |
| Chlorophyll-a (Algae) | 55.2 µg/L | F |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Jefferson Lake
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Fishing Jefferson Lake
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | → Stable | -0.3 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -7.97 µg/L/yr | 2 |
Location
County Ranking
Ranked #5 of 5 lakes in St. Louis city County
Cleaner Lakes Within 30 Miles
Jefferson Lake holds Grade D. 5 nearby lakes hold higher grades.
- DO'Fallon Park LakeSt. Louis city County · 4.1 mi · Higher overall water quality score
- DBoathouse LakeSt. Louis city County · 5 mi · Higher overall water quality score
- DForest Park PondSt. Louis city County · 1 mi · Higher overall water quality score
- DLafayette Park LakeSt. Louis city County · 3.2 mi · Higher overall water quality score
- DSimpson Park LakeSt. Louis County · 11.8 mi · Higher overall water quality score
Nearby Lakes in St. Louis city County
Explore Jefferson 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
1 EPA-permitted facility operate within about 5 miles of Jefferson Lake under Clean Water Act (NPDES) discharge permits.
- Solae LlcSt. Louis · 0.9 mi away · NPDES MONX00102
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: 2020-08-24
Monitoring stations: 1