Fon-du-Lac Reservoir
Jefferson County, Missouri26 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- #4 of 4 in the county
- 34 ft max depth
Fon-du-Lac Reservoir in Jefferson County, Missouri has a water quality grade of F (Algae-prone). Water clarity: 1.3 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Surface area: 26 acres.
- Clarity
- 1.3 ft
- Typical in September
- 81°F
- Max depth
- ~34 ft est.
- Area
- 26 acres
- Type
- Hypereutrophic
- Trend
- ↓ Declining
Stays via Stay22
Stays near Fon-du-Lac Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Fon-du-Lac Reservoir in Jefferson 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 Fon-du-Lac Reservoir are listed below.
Top-rated places to stay near Fon-du-Lac Reservoir
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Watch Fon-du-Lac Reservoir’s letter
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Fon-du-Lac Reservoir is a 26-acre highly nutrient-loaded hypereutrophic lake in Jefferson County, Missouri with an estimated average depth of about 34 feet. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 3 other monitored lakes in Jefferson County, Fon-du-Lac Reservoir ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-21. 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 F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.3 ft of visibility. Phosphorus 81 µg/L. Chlorophyll-a 40.7 µg/L. TSI 69. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.3 ft | Not graded |
| Phosphorus | 81 µg/L | Poor |
| Chlorophyll-a (Algae) | 40.7 µg/L | Poor |
| Trophic State Index (TSI) | 69 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Fon-du-Lac Reservoir typically sits around 81°F at the surface in September. Summer average is about 85°F. Usually warmest in Jul (about 87°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 23 field readings (2022–2024) via the EPA Water Quality Portal. See the full Fon-du-Lac Reservoir water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~34 ft est. |
| Average Depth | ~13 ft est. |
| Surface Area | 26 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Missouri has not published bathymetry for Fon-du-Lac Reservoir.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Fon-du-Lac Reservoir
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.075 m/yr | 3 |
| Phosphorus | ↓ Declining | +53.5 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -6.65 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Fon-du-Lac Reservoir is a man-made reservoir impounded by the Fondulac Dam (completed 1954), built primarily for recreation on the TR- SALINE CREEK; earth-type dam, 28 ft tall.
- Surface area
- 26 ac
- Normal storage
- 296 ac-ft
- Max storage
- 389 ac-ft
- Drainage area
- 346 sq mi
- Hazard class
- High
- Owner
- TRUSTEES-FON-DU-LAC SUBD
Source: USACE National Inventory of Dams, NID ID MO10699 · Operator website
Regulated Pollution Sources Nearby
34 EPA-permitted facilities operate within about 5 miles of Fon-du-Lac Reservoir under Clean Water Act (NPDES) discharge permits, including 2 classified by the EPA as major dischargers. 20 facilities have a reported Clean Water Act violation in the past three years.
- Npsd Interim Saline Creek Regional WwtpFenton · 3.4 mi away · NPDES MO0128490MajorRecent violation
- Msd Fenton WwtpFenton · 2.6 mi away · NPDES MO0086126Major
- Npsd Terry Jean Acres WwtpFenton · 1.4 mi away · NPDES MO0092649Recent violation
- Fenton United Methodist CFenton · 1.5 mi away · NPDES MO0098850Recent violation
- Koller Craft Plastic ProductsFenton · 1.6 mi away · NPDES MO0123358Recent violation
- Sir Thomas Manor AptsFenton · 1.8 mi away · NPDES MO0088897Recent violation
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 #4 of 4 lakes in Jefferson County
Nearby Lakes With Higher Grades
Fon-du-Lac Reservoir holds Grade F. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Jefferson County
Frequently asked questions about Fon-du-Lac Reservoir
Where is Fon-du-Lac Reservoir?
- Fon-du-Lac Reservoir is a lake in Jefferson County, Missouri. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Fon-du-Lac Reservoir?
- Fon-du-Lac Reservoir in Jefferson County, Missouri has a water quality grade of F (Algae-prone). Water clarity: 1.3 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Surface area: 26 acres.
Is Fon-du-Lac Reservoir safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Fon-du-Lac Reservoir?
- Fon-du-Lac Reservoir typically sits around 81°F at the surface in September, from 23 EPA Water Quality Portal field readings (2022–2024). That is a typical value for the month, not a live reading.
How deep is Fon-du-Lac Reservoir?
- No published bathymetric survey covers Fon-du-Lac Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 34 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 26 acres.
Explore Fon-du-Lac Reservoir across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Missouri's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
Missouri's cleanest and most-polluted lakes, ranked
Planning a trip around Gateway Arch?
Fon-du-Lac Reservoir is about 18 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 F Lakes in Missouri
Hypereutrophic Lakes in Missouri
Where this data comes from
68 measurements from 1 monitoring station, 2022–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC68 samples · 2022–2024
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)
Lake size & watershed from HydroLAKES (HydroSHEDS)