Boathouse 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 2024. Phosphorus level is improving over recent sampling years. Compared to the 4 other monitored lakes in St. Louis city County, Boathouse Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-11. 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 2.3 ft of visibility. Phosphorus level: 59.8 µg/L. Chlorophyll-a: 18 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.3 ft | F |
| Phosphorus | 59.8 µg/L | C |
| Chlorophyll-a (Algae) | 18 µg/L | C |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Boathouse Lake
Compare lakeside cabins, hotels, and vacation rentals near Boathouse Lake in St. Louis city County, Missouri — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Fishing Boathouse Lake
Water Quality Trend: → Stable
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.009 m/yr | 5 |
| Phosphorus | ↑ Improving | -1.45 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +3.12 µg/L/yr | 5 |
Water Temperature
Boathouse Lake averages about 83°F at the surface in summer, usually warmest in Jul (about 84°F) and coldest in Apr (about 62°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 48 field readings (2019–2024) via the EPA Water Quality Portal. See the full Boathouse Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 5 lakes in St. Louis city County
Nearby Lakes in St. Louis city County
Explore Boathouse 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
Franklin County · Clarity: 2.6 ft
St. Charles County · Clarity: 2.7 ft
St. Charles County · Clarity: 3.2 ft
St. Charles County · Clarity: 2.6 ft
Eutrophic Lakes in Missouri
More records, surveys & data sources
Regulated Pollution Sources Nearby
12 EPA-permitted facilities operate within about 5 miles of Boathouse Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 4 facilities have a reported Clean Water Act violation in the past three years.
- Msd Lemay WwtpSt. Louis · 2.7 mi away · NPDES MO0025151Major
- Dupo Stp, Village OfDupo · 1.7 mi away · NPDES IL0026441Recent violation
- Acbl Transportation Services LlcSt. Louis · 1.7 mi away · NPDES MO0001601Recent violation
- American River TransportSt. Louis · 2 mi away · NPDES MO0138975Recent violation
- Dupo TerminalDupo · 4.2 mi away · NPDES IL0045284Recent violation
- Mdanda Turbine Generator Repair FacilitySt Louis · 1.1 mi away · NPDES MONX00812
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: 2024-09-11
Monitoring stations: 1