Lake St. Louis by Dam is a 563-acre productive, nutrient-rich eutrophic lake in St. Charles County, Missouri. Water quality is graded F based on 3 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 10 other monitored lakes in St. Charles County, Lake St. Louis by Dam ranks #9 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-15. Grade methodology: LakeGrade methodology.
Watch Lake St. Louis by Dam water quality
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 2.3 ft of visibility. Phosphorus level: 74.8 µg/L. Chlorophyll-a: 32.2 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.3 ft | F |
| Phosphorus | 74.8 µg/L | D |
| Chlorophyll-a (Algae) | 32.2 µg/L | F |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 563 acres |
Where to stay near Lake St. Louis by Dam
Compare lakeside cabins, hotels, and vacation rentals near Lake St. Louis by Dam in St. Charles 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 Lake St. Louis by Dam
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.055 m/yr | 5 |
| Phosphorus | → Stable | +1.2 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +2.21 µg/L/yr | 5 |
Water Temperature
Lake St. Louis by Dam averages about 80°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in Apr (about 64°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 53 field readings (2010–2024) via the EPA Water Quality Portal. See the full Lake St. Louis by Dam water temperature breakdown →
Location
County Ranking
Ranked #9 of 11 lakes in St. Charles County
Cleaner Lakes Within 30 Miles
Lake St. Louis by Dam holds Grade F. 3 nearby lakes hold higher grades.
- DL. Ste. Louise LakeSt. Charles County · 1.4 mi · Higher grade (F → D)
- DL. Ste. Louise LakeSt. Charles County · 1.9 mi · Higher grade (F → D)
- DLake St. LouisSt. Charles County · 0.1 mi · Higher grade (F → D)
Nearby Lakes in St. Charles County
Explore Lake St. Louis by Dam across LakeGrade
More Missouri Lake Rankings
Other Grade F Lakes in Missouri
St. Louis County · Clarity: 1.9 ft
St. Louis County · Clarity: 1.2 ft
St. Louis County · Clarity: 1.6 ft
Jefferson County · Clarity: 1.3 ft
St. Louis County · Very Poor
St. Louis County · Clarity: 3.1 ft
Eutrophic Lakes in Missouri
Compare Lake St. Louis by Dam With Nearby Lakes
More records, surveys & data sources
Reservoir Info (USACE NID)
Lake St. Louis by Dam is a man-made reservoir impounded by the Lake St. Louis Dam (completed 1973), built primarily for recreation on the PERUQUE CREEK; earth-type dam, 47 ft tall and 900 ft long.
- Surface area
- 563 ac
- Normal storage
- 6,300 ac-ft
- Max storage
- 14,650 ac-ft
- Drainage area
- 56.41 sq mi
- Hazard class
- High
- Owner
- LAKE ST LOUIS COMM ASSOC
Source: USACE National Inventory of Dams, NID ID MO10545 · Operator website · Matched by proximity (0.16 km)
EPA Impairment Status
Lake St. Louis by Dam 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_7054.00 · Official waterbody report · Matched by proximity (1.54 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Lake St. Louis by Dam under Clean Water Act (NPDES) discharge permits.
- R An E Sanitary LandfillO'Fallon · 1 mi away · NPDES MO0121231
- Pittsburgh Glass Works LlcO'Fallon · 1.1 mi away · NPDES MONX00149
- Inc Environmental Recycling LlcO'Fallon · 1.2 mi away · NPDES MONX00623
- King InnovationO'Fallon · 2.1 mi away · NPDES MONX00906
- Laclede MhpO'Fallon · 3.6 mi away · NPDES MO0081540
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
Most recent sample: 2024-09-15
Monitoring stations: 1