Corydon Reservoir
Wayne County, Iowa67 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Pesticides
- #2 of 3 in the county
- 21 ft max depth
- Limited data
Corydon Reservoir in Wayne County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.9 ft visibility. Phosphorus: 612 µg/L. Chlorophyll-a (algae): 44 µg/L. Surface area: 66.9 acres.
- Clarity
- 1.9 ft
- Max depth
- ~21 ft est.
- Area
- 67 acres
- Type
- Hypereutrophic
- Trend
- ↓ Declining
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Stays near Corydon Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Corydon Reservoir in Wayne County, Iowa — 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 Corydon Reservoir are listed below.
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Watch Corydon Reservoir’s letter
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Free interactive depth-contour map of Corydon Reservoir, reaching a maximum surveyed depth of 10 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Corydon Reservoir is a 67-acre highly nutrient-loaded hypereutrophic lake in Wayne County, Iowa with an estimated average depth of about 21 feet. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 2 other monitored lakes in Wayne County, Corydon Reservoir ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-09. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
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. Corydon Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for pesticides. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.9 ft of visibility. Phosphorus 612 µg/L. Chlorophyll-a 44 µg/L. TSI 77. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.9 ft | Not graded |
| Phosphorus | 612 µg/L | Poor |
| Chlorophyll-a (Algae) | 44 µg/L | Poor |
| Trophic State Index (TSI) | 77 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~21 ft est. |
| Average Depth | ~11 ft est. |
| Surface Area | 67 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Iowa has not published bathymetry for Corydon Reservoir.
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.
Fishing Corydon Reservoir
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.14 m/yr | 2 |
| Phosphorus | ↑ Improving | -205.5 µg/L/yr | 2 |
| Chlorophyll-a | ↓ Declining | +14 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Corydon Reservoir is a man-made reservoir impounded by the Corydon Reservoir Dam (completed 1974), built primarily for recreation on the TR-WEST JACKSON CREEK; earth-type dam, 26 ft tall and 750 ft long.
- Surface area
- 66.9 ac
- Normal storage
- 420 ac-ft
- Max storage
- 870 ac-ft
- Drainage area
- 2.7 sq mi
- Hazard class
- Significant
- Owner
- City of Corydon
Source: USACE National Inventory of Dams, NID ID IA01641 · Operator website
EPA Impairment Status
Corydon Reservoir 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 IA 05-CHA-1331 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Corydon Reservoir under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Corydon City Of StpCorydon · 0.8 mi away · NPDES IA0049573Recent 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.
County Ranking
Ranked #2 of 3 lakes in Wayne County
Nearby Lakes With Higher Grades
Corydon Reservoir holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Wayne County
Frequently asked questions about Corydon Reservoir
Where is Corydon Reservoir?
- Corydon Reservoir is a lake in Wayne County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Corydon Reservoir?
- Corydon Reservoir in Wayne County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.9 ft visibility. Phosphorus: 612 µg/L. Chlorophyll-a (algae): 44 µg/L. Surface area: 66.9 acres.
Is Corydon Reservoir safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Corydon Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for pesticides. Check local advisories before you swim.
How deep is Corydon Reservoir?
- No published bathymetric survey covers Corydon Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 21 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 66.9 acres.
Explore Corydon Reservoir across LakeQuality
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
Where this data comes from
30 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX30 samples · 2023–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- In-Vitro Determination of Chlorophyll
- ISU modification of APHA 2130-B
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)