Marion Reservoir
Franklin County, Missouri7 acresView mapDirections
Missouri DNR publishes the water-quality measurements for Marion Reservoir. Here is what has been measured.
- Limited data
Marion Reservoir in Franklin County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. Water clarity: 5.9 ft visibility. Phosphorus: 16 µg/L. Chlorophyll-a (algae): 9.8 µg/L. Surface area: 7 acres.
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. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Marion 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 Marion Reservoir
These are the measurements Missouri DNR publishes for Marion Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.9 ft. Phosphorus 16 µg/L. Chlorophyll-a 9.8 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.9ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 16µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 9.8µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Marion Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
7 acres
No bathymetric survey has been published for Marion Reservoir, so its depth is not documented here.
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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.
Nearby Lakes in Franklin County
Frequently asked questions about Marion Reservoir
Where is Marion Reservoir?
- Marion Reservoir is a lake in Franklin County, Missouri. Its water-quality measurements are published by Missouri DNR and shown on this page as reported.
What is the water quality of Marion Reservoir?
- Marion Reservoir in Franklin County, Missouri has water-quality measurements published by Missouri DNR, shown here as reported. 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?
- Nutrient and algae readings are 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 lakes in Missouri
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)
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)