Simpson Park Lake is a productive, nutrient-rich eutrophic lake in St. Louis County, Missouri. Water quality is graded D based on 3 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 8 other monitored lakes in St. Louis County, Simpson Park Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-20. 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 1.8 ft of visibility. Phosphorus level: 73 µg/L. Chlorophyll-a: 23.3 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.8 ft | F |
| Phosphorus | 73 µg/L | D |
| Chlorophyll-a (Algae) | 23.3 µg/L | D |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Simpson Park Lake
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Fishing Simpson Park Lake
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.004 m/yr | 4 |
| Phosphorus | ↑ Improving | -3.9 µg/L/yr | 4 |
| Chlorophyll-a | → Stable | -0.42 µg/L/yr | 4 |
Recreation & Access
Water Temperature
Simpson Park Lake averages about 84°F at the surface in summer, usually warmest in Aug (about 85°F) and coldest in Apr (about 66°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 50 field readings (2010–2024) via the EPA Water Quality Portal. See the full Simpson Park Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 9 lakes in St. Louis County
Cleaner Lakes Within 30 Miles
Simpson Park Lake holds Grade D. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in St. Louis County
Explore Simpson Park Lake across LakeGrade
More Missouri Lake Rankings
Other Grade D Lakes in Missouri
St. Louis city County · Clarity: 1.6 ft
St. Louis city County · Clarity: 2.3 ft
St. Louis city County · Poor
St. Louis city County · Clarity: 2.3 ft
St. Louis city County · Clarity: 1.6 ft
Franklin County · Clarity: 2.6 ft
Eutrophic Lakes in Missouri
More records, surveys & data sources
EPA Impairment Status
Simpson Park Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MO_7502.00 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
22 EPA-permitted facilities operate within about 5 miles of Simpson Park Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Mdc, Powder Valley Nature CenterKirkwood · 1.9 mi away · NPDES MO0109975Recent violation
- Bohn And Dawson, IncorporatedSt. Louis · 0.3 mi away · NPDES MONX00752
- Bohn And Dawson, Inc.Kirkwood · 0.3 mi away · NPDES MO0001627
- Basf Agricultural Solutions Us LlcSt. Louis · 0.4 mi away · NPDES MONX00689
- Daimler Chrysler St. LouiFenton · 0.5 mi away · NPDES MO0000167
- Bausch And LombSt. Louis · 0.5 mi away · NPDES MONX00077
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2024-09-20
Monitoring stations: 1