L Ste Louise Lake
St. Charles County, Missouri70 acresView mapDirections
Nutrients and algae sit mid-range for this region.
↑ up from D at the last regrade
- Eutrophic
- Impaired · Mercury
- #2 of 6 in the county
L Ste Louise Lake in St. Charles County, Missouri has a water quality grade of C (Fair). Water clarity: 3.2 ft visibility. Phosphorus: 33.5 µg/L. Chlorophyll-a (algae): 17.2 µg/L. Surface area: 70 acres.
- Clarity
- 3.2 ft
- Typical in September
- 77°F
- Area
- 70 acres
- Type
- Eutrophic
- Phosphorus
- 33.5 µg/L
- Chlorophyll-a
- 17.2 µg/L
- Trend
- ↓ Declining
Stays via Stay22
Stays near L Ste Louise Lake
Compare lakeside cabins, hotels, and vacation rentals near L Ste Louise Lake 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.
Top-rated places to stay near L Ste Louise 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 L Ste Louise Lake’s letter
Email me if this lake’s grade moves. Grades stay free.
Or email
L Ste Louise Lake is a 70-acre productive, nutrient-rich eutrophic lake in St. Charles County, Missouri. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 5 other monitored lakes in St. Charles County, L Ste Louise Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-15. 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 C is nutrients and algae, not a swimming clearance. L Ste Louise Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Very murky, less than 3.2 ft of visibility. Phosphorus 33.5 µg/L. Chlorophyll-a 17.2 µg/L. TSI 58. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.2 ft | Not graded |
| Phosphorus | 33.5 µg/L | Good |
| Chlorophyll-a (Algae) | 17.2 µg/L | Fair |
| Trophic State Index (TSI) | 58 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
L Ste Louise Lake typically sits around 77°F at the surface in September. Summer average is about 82°F. Usually warmest in Jul (about 83°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 86 field readings (2010–2024) via the EPA Water Quality Portal. See the full L Ste Louise Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 70 acres |
No bathymetric survey has been published for L Ste Louise Lake, so its depth is not documented here.
Fishing L Ste Louise Lake
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.03 m/yr | 5 |
| Phosphorus | → Stable | -0.47 µg/L/yr | 5 |
| Chlorophyll-a | ↓ Declining | +1.19 µg/L/yr | 5 |
Reservoir Info (USACE NID)
L Ste Louise Lake is a man-made reservoir impounded by the Lake Sainte Louise Dam (completed 1967), built primarily for recreation on the BRANCH PERUQUE CREEK; earth-type dam, 52 ft tall and 790 ft long.
- Surface area
- 70 ac
- Normal storage
- 1,170 ac-ft
- Max storage
- 1,420 ac-ft
- Drainage area
- 1.04 sq mi
- Hazard class
- High
- Owner
- LAKE SAINT LOUIS COMM.
Source: USACE National Inventory of Dams, NID ID MO10490 · Operator website · Matched by proximity (0.12 km)
EPA Impairment Status
L Ste Louise 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_7055.00 · Official waterbody report · Matched by proximity (0.56 km)
County Ranking
Ranked #2 of 6 lakes in St. Charles County
Nearby Lakes in St. Charles County
Frequently asked questions about L Ste Louise Lake
Where is L Ste Louise Lake?
- L Ste Louise Lake is a lake in St. Charles County, Missouri. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for L Ste Louise Lake?
- L Ste Louise Lake in St. Charles County, Missouri has a water quality grade of C (Fair). Water clarity: 3.2 ft visibility. Phosphorus: 33.5 µg/L. Chlorophyll-a (algae): 17.2 µg/L. Surface area: 70 acres.
Is L Ste Louise Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. L Ste Louise Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
What is the water temperature of L Ste Louise Lake?
- L Ste Louise Lake typically sits around 77°F at the surface in September, from 86 EPA Water Quality Portal field readings (2010–2024). That is a typical value for the month, not a live reading.
Explore L Ste Louise Lake across LakeQuality
Planning a trip around Gateway Arch?
L Ste Louise Lake is about 35 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 C Lakes in Missouri
Eutrophic Lakes in Missouri
Where this data comes from
125 measurements from 2 monitoring stations, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC119 samples · 2020–2024 - Missouri Dept. of Natural Resources
MDNR6 samples · 2022
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
- Nitrogen and Phosphorus, Total, Whole-water, Alkaline Persulfate Digest
Monitoring station identifiers (2)
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
Impairment status from EPA ATTAINS 303(d) database