Marion Reservoir
Franklin County, Missouri7 acresView mapDirections
Not enough samples to grade — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). No letter yet. Here is what we do have.
- Limited data
Marion Reservoir in Franklin County, Missouri is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 5.9 ft visibility. Phosphorus: 16 µg/L. Chlorophyll-a (algae): 9.8 µg/L. Surface area: 7 acres.
- Clarity
- 5.9 ft
- Area
- 7 acres
- Phosphorus
- 16 µg/L
- Chlorophyll-a
- 9.8 µg/L
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Watch Marion Reservoir’s letter
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Why Marion Reservoir has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Marion Reservoir, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity, phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Missouri DNR and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Marion Reservoir is a 7-acre lake in Franklin County, Missouri.
Source: EPA Water Quality Portal sampling records, Missouri DNR, last sampled 2021-08-14. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Marion Reservoir
These readings exist but are not enough for an A–F grade — see why.
Murky, only visible to about 5.9 ft. Phosphorus 16 µg/L. Chlorophyll-a 9.8 µg/L. TSI 50.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.9 ft | Not graded |
| Phosphorus | 16 µg/L | Not graded |
| Chlorophyll-a (Algae) | 9.8 µg/L | Not graded |
| Trophic State Index (TSI) | 50 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 7 acres |
No bathymetric survey has been published for Marion Reservoir, so its depth is not documented here.
Fishing Marion Reservoir
Reservoir Info (USACE NID)
Marion Reservoir is a man-made reservoir impounded by the Lake Marion Dam (completed 1965), built primarily for recreation on the TR TO CLAVEY CREEK; earth-type dam, 30 ft tall.
- Surface area
- 7 ac
- Normal storage
- 70 ac-ft
- Max storage
- 112 ac-ft
- Drainage area
- 100 sq mi
- Hazard class
- Low
- Owner
- CALVEY LAKE SUBDV HMOWNS
Source: USACE National Inventory of Dams, NID ID MO30571 · Operator website
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Marion Reservoir under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Calvey Brook Estates WwtpRobertsville · 3.2 mi away · NPDES MO0130095Recent 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.
Graded lakes near Marion Reservoir
Marion Reservoir has no grade, but these lakes within a short drive do.
Nearby Lakes in Franklin County
Frequently asked questions about Marion Reservoir
Where is Marion Reservoir?
- Marion Reservoir is a lake in Franklin County, Missouri. LakeQuality has not rated this lake (UNRATED) — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
What is the water quality grade for Marion Reservoir?
- Marion Reservoir in Franklin County, Missouri is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 5.9 ft visibility. Phosphorus: 16 µg/L. Chlorophyll-a (algae): 9.8 µg/L. Surface area: 7 acres.
Is Marion Reservoir safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
Explore Marion Reservoir across LakeQuality
Planning a trip around Gateway Arch?
Marion Reservoir is about 36 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 Lakes in Missouri
Mesotrophic Lakes in Missouri
Where this data comes from
3 measurements from 1 monitoring station, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Univ. of Missouri, Columbia
UMC3 samples · 2021
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)