Jefferson Lake
St. Louis city County, MissouriView mapDirections
Missouri DNR publishes the water-quality measurements for Jefferson Lake. Here is what has been measured.
- Limited data
Jefferson Lake in St. Louis city County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Phosphorus: 70 µg/L. Chlorophyll-a (algae): 55.2 µg/L.
Jefferson Lake is a lake in St. Louis city County, Missouri. Overall water quality is improving over recent sampling years.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2020-08-24. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Jefferson Lake is safe to swim in today is a call for the Missouri Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Jefferson Lake
These are the measurements Missouri DNR publishes for Jefferson Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 70 µg/L. Chlorophyll-a 55.2 µg/L. TSI 68.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 70µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 55.2µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 68 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Jefferson Lake
Answers come straight from the public measurements and survey records on this page.
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Stays near Jefferson Lake
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Fishing Jefferson Lake
Water quality readings over time
2 seasons of samples on record (2020–2024). Calling a direction takes at least 4 years of the same measurement.
Phosphorus
Stable-0.3 µg/L/yr2 years
Chlorophyll-a
Improving-7.97 µg/L/yr2 years
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.
Nearby Lakes in St. Louis city County
Frequently asked questions about Jefferson Lake
Where is Jefferson Lake?
- Jefferson Lake is a lake in St. Louis city County, Missouri. Its water-quality measurements are published by Missouri DNR and shown on this page as reported.
What is the water quality of Jefferson Lake?
- Jefferson Lake in St. Louis city County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Phosphorus: 70 µg/L. Chlorophyll-a (algae): 55.2 µg/L.
Is Jefferson Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Jefferson Lake across LakeQuality
Planning a trip around Gateway Arch?
Jefferson Lake is about 4 miles from Gateway Arch National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Gateway Arch →More lakes in Missouri
Other Lakes in Missouri
Eutrophic Lakes in Missouri
Where this data comes from
2 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Missouri Dept. of Natural Resources
MDNR2 samples · 2020
Analytical methods
- Nitrogen and Phosphorus, Total, Whole-water, Alkaline Persulfate Digest
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)