Fon-du-Lac Reservoir
Jefferson County, Missouri26 acresView mapDirections
Missouri DNR publishes the water-quality measurements for Fon-du-Lac Reservoir. Here is what has been measured.
- Hypereutrophic
- 34 ft max depth
Fon-du-Lac Reservoir in Jefferson County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Water clarity: 1.3 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Surface area: 26 acres.
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. 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. 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. Check local advisories before you swim.
Whether Fon-du-Lac Reservoir 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 Fon-du-Lac Reservoir
These are the measurements Missouri DNR publishes for Fon-du-Lac Reservoir, 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 1.3 ft of visibility. Phosphorus 81 µg/L. Chlorophyll-a 40.7 µg/L. TSI 69.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 81µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 40.7µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 69 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Fon-du-Lac Reservoir
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (64°F) to its warmest (87°F).
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
Max depth
~34 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
Watershed (drainage) area
0 sq mi
HydroLAKES / HydroSHEDS
Shoreline
0.9 mi
HydroLAKES / HydroSHEDS
Elevation
518 ft
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.
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 readings cover 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
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Fishing Fon-du-Lac Reservoir
Water quality readings over time
3 seasons of samples on record (2022–2024). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening3 years
Phosphorus
Worsening+53.5 µg/L/yr3 years
Chlorophyll-a
Improving-6.65 µg/L/yr3 years
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.
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. Its water-quality measurements are published by Missouri DNR and shown on this page as reported.
What is the water quality of Fon-du-Lac Reservoir?
- Fon-du-Lac Reservoir in Jefferson County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. 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?
- Nutrient and algae readings are 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
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 lakes in Missouri
Other 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)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)