Marion Lake
Marion County, Kansas6,210 acresView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #1 of 2 in the county
- 78 ft max depth
- Public access
Marion Lake in Marion County, Kansas has a water quality grade of F (Algae-prone). Water clarity: 2 ft visibility. Phosphorus: 230 µg/L. Chlorophyll-a (algae): 36.3 µg/L. Surface area: 6210 acres.
- Clarity
- 2 ft
- Max depth
- ~78 ft est.
- Area
- 6,210 acres
- Type
- Hypereutrophic
- Phosphorus
- 230 µg/L
- Chlorophyll-a
- 36.3 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Marion Lake
Compare lakeside cabins, hotels, and vacation rentals near Marion Lake in Marion County, Kansas — 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 Marion Lake are listed below.
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Watch Marion Lake’s letter
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Marion Lake is a 6,210-acre highly nutrient-loaded hypereutrophic lake in Marion County, Kansas with an estimated average depth of about 78 feet. Water quality is graded F based on 2 sampling years through 2022. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 3 public boat landings. Compared to the 1 other monitored lakes in Marion County, Marion Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, KDHE, last sampled 2022-08-04. Grade methodology: LakeQuality methodology.
What Marion Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch3 documented ramps
- Big water6,210 acres
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. Marion Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 2 ft of visibility. Phosphorus 230 µg/L. Chlorophyll-a 36.3 µg/L. TSI 72. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2 ft | Not graded |
| Phosphorus | 230 µg/L | Poor |
| Chlorophyll-a (Algae) | 36.3 µg/L | Poor |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~78 ft est. |
| Average Depth | ~31 ft est. |
| Surface Area | 6,210 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Kansas has not published bathymetry for Marion Lake.
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.
Recreation & Access
- Marion-French CreekPublic
- Marion-Cotton WoodPublic
- Marion-HillsboroPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Marion Lake
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.208 m/yr | 3 |
| Phosphorus | ↑ Improving | -15 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -3.04 µg/L/yr | 3 |
Reservoir Info (USACE NID)
Marion Lake is a man-made reservoir impounded by the Marion Dam (completed 1968), built primarily for flood risk reduction on the Cottonwood River; gravity-type dam, 67 ft tall and 8,375 ft long.
- Surface area
- 6,210 ac
- Normal storage
- 80,680 ac-ft
- Max storage
- 189,200 ac-ft
- Drainage area
- 200 sq mi
- Hazard class
- High
- Owner
- USACE - Tulsa District
All listed purposes: Flood Risk Reduction;Other;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID KS00006 · Operator website
EPA Impairment Status
Marion Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit KS-LM020001 · Official waterbody report
County Ranking
Ranked #1 of 2 lakes in Marion County
Nearby Lakes in Marion County
Frequently asked questions about Marion Lake
Where is Marion Lake?
- Marion Lake is a lake in Marion County, Kansas. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Marion Lake?
- Marion Lake in Marion County, Kansas has a water quality grade of F (Algae-prone). Water clarity: 2 ft visibility. Phosphorus: 230 µg/L. Chlorophyll-a (algae): 36.3 µg/L. Surface area: 6210 acres.
Is Marion Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Marion Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Marion Lake?
- No published bathymetric survey covers Marion Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 78 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 6210 acres.
Are there boat ramps on Marion Lake?
- Marion Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Marion-French Creek, Marion-Cotton Wood, Marion-Hillsboro. Public access is listed as yes.
Explore Marion Lake across LakeQuality
More Kansas Lake Rankings
Other Grade F Lakes in Kansas
Hypereutrophic Lakes in Kansas
Where this data comes from
26 measurements from 6 monitoring stations, 2014–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Kansas Water Science Center
USGS-KS15 samples · 2022 - Kansas Department Of Health And Environment
21KAN001_WQX11 samples · 2014–2017
Analytical methods
- Plant pigments, sonication & 445
- YSI EXO turbidity sensor, FNU
- Depth, Secchi disk depth
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (6)
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory