Fon-du-Lac Reservoir is a 26-acre productive, nutrient-rich eutrophic lake in Jefferson 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 6 other monitored lakes in Jefferson County, Fon-du-Lac Reservoir ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2024-09-21. Grade methodology: LakeGrade methodology.
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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 1.3 ft of visibility. Phosphorus level: 81 µg/L. Chlorophyll-a: 40.7 µg/L. Trophic State Index: 69.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.3 ft | F |
| Phosphorus | 81 µg/L | D |
| Chlorophyll-a (Algae) | 40.7 µg/L | F |
| Trophic State Index (TSI) | 69 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 26 acres |
Where to stay 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.
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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 |
Water Temperature
Fon-du-Lac Reservoir averages about 85°F at the surface in summer, 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 →
Location
County Ranking
Ranked #7 of 7 lakes in Jefferson County
Cleaner Lakes Within 30 Miles
Fon-du-Lac Reservoir holds Grade F. 4 nearby lakes hold higher grades.
- CLake Tishomingo Nr. DamJefferson County · 13.9 mi · Two grade letters higher (F → C)
- DBoathouse LakeSt. Louis city County · 12.1 mi · Higher grade (F → D)
- DSimpson Park LakeSt. Louis County · 4.6 mi · Higher grade (F → D)
- DSimpson Park LakeSt. Louis County · 4.7 mi · Higher grade (F → D)
Nearby Lakes in Jefferson County
Explore Fon-du-Lac Reservoir across LakeGrade
More Missouri Lake Rankings
Other Grade F Lakes in Missouri
St. Louis County · Clarity: 0.6 ft
St. Louis County · Very Poor
St. Louis County · Clarity: 1.9 ft
St. Louis County · Clarity: 1.6 ft
St. Louis County · Clarity: 1.2 ft
St. Louis County · Clarity: 3.1 ft
Eutrophic Lakes in Missouri
More records, surveys & data sources
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
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-21
Monitoring stations: 1