L Ste Louise Lake
St. Charles County, Missouri70 acresView mapDirections
Missouri DNR publishes the water-quality measurements for L Ste Louise Lake. Here is what has been measured.
- Eutrophic
- Impaired · Mercury
L Ste Louise Lake in St. Charles County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Water clarity: 3.2 ft visibility. Phosphorus: 33.5 µg/L. Chlorophyll-a (algae): 17.2 µg/L. Surface area: 70 acres.
L Ste Louise Lake is a 70-acre productive, nutrient-rich eutrophic lake in St. Charles County, Missouri. 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. Methodology: how these readings are compared.
Swimming conditions
Readings onlyAlgae risk
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are 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.
Whether L Ste Louise Lake is safe to swim in today is a call for the Missouri Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for L Ste Louise Lake
These are the measurements Missouri DNR publishes for L Ste Louise Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 3.2 ft of visibility. Phosphorus 33.5 µg/L. Chlorophyll-a 17.2 µg/L. TSI 58.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 3.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 33.5µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 17.2µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 58 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about L Ste Louise Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (64°F) to its warmest (83°F).
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
Surface area
70 acres
No bathymetric survey has been published for L Ste Louise Lake, so its depth is not documented here.
Stays via Stay22
Stays near L Ste Louise Lake
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Fishing L Ste Louise Lake
Water Quality Trend: Worsening
Based on 5 years of monitoring (2020–2024).
Water clarity
Worsening5 years
Phosphorus
Stable-0.47 µg/L/yr5 years
Chlorophyll-a
Worsening+1.19 µg/L/yr5 years
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
Designated uses not supporting: Fish consumption.
Source: EPA ATTAINS assessment unit MO_7055.00 · Official waterbody report
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. Its water-quality measurements are published by Missouri DNR and shown on this page as reported.
What is the water quality of L Ste Louise Lake?
- L Ste Louise Lake in St. Charles County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. 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?
- Nutrient and algae readings are 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 lakes in Missouri
Other 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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database