Boathouse Lake
St. Louis city County, MissouriView mapDirections
Nutrients and algae run above the regional average.
- Eutrophic
- #1 of 3 in the county
Boathouse Lake in St. Louis city County, Missouri has a water quality grade of D (Nutrient-rich). Water clarity: 2.3 ft visibility. Phosphorus: 59.8 µg/L. Chlorophyll-a (algae): 18 µg/L.
- Clarity
- 2.3 ft
- Typical in September
- 80°F
- Type
- Eutrophic
- Phosphorus
- 59.8 µg/L
- Chlorophyll-a
- 18 µg/L
- Trend
- → Stable
Stays via Stay22
Stays 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Boathouse Lake are listed below.
Top-rated places to stay near Boathouse Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Missouri’s top lakes →
Watch Boathouse Lake’s letter
Email me if this lake’s grade moves. Grades stay free.
Or email
Boathouse 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 2024. Phosphorus level is improving over recent sampling years. Compared to the 2 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: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2.3 ft of visibility. Phosphorus 59.8 µg/L. Chlorophyll-a 18 µg/L. TSI 62. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.3 ft | Not graded |
| Phosphorus | 59.8 µg/L | Poor |
| Chlorophyll-a (Algae) | 18 µg/L | Fair |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Boathouse Lake typically sits around 80°F at the surface in September. Summer average is about 83°F. 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 →
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 |
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.
County Ranking
Ranked #1 of 3 lakes in St. Louis city County
Nearby Lakes in St. Louis city County
Frequently asked questions about Boathouse Lake
Where is Boathouse Lake?
- Boathouse Lake is a lake in St. Louis city County, Missouri. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Boathouse Lake?
- Boathouse Lake in St. Louis city County, Missouri has a water quality grade of D (Nutrient-rich). Water clarity: 2.3 ft visibility. Phosphorus: 59.8 µg/L. Chlorophyll-a (algae): 18 µg/L.
Is Boathouse Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Boathouse Lake?
- Boathouse Lake typically sits around 80°F at the surface in September, from 48 EPA Water Quality Portal field readings (2019–2024). That is a typical value for the month, not a live reading.
Explore Boathouse Lake across LakeQuality
Planning a trip around Gateway Arch?
Boathouse Lake is about 6 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 Missouri Lake Rankings
Other Grade D Lakes in Missouri
Eutrophic Lakes in Missouri
Where this data comes from
105 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC105 samples · 2020–2024
Analytical methods
- Depth, Secchi disk in meters
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)