Corydon Reservoir is a 67-acre productive, nutrient-rich eutrophic lake in Wayne County, Iowa. 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: 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 1.9 ft of visibility. Chlorophyll-a: 44 µg/L. Trophic State Index: 68.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.9 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 44 µg/L | F |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 67 acres |
Where to stay near Corydon Reservoir
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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 |
| Chlorophyll-a | ↓ Declining | +14 µg/L/yr | 2 |
Location & Depth Map
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.
County Ranking
Ranked #2 of 3 lakes in Wayne County
Cleaner Lakes Within 30 Miles
Corydon Reservoir holds Grade F. 2 nearby lakes hold higher grades.
- DBob White LakeWayne County · 4.2 mi · Higher grade (F → D)
- DRathbun LakeAppanoose County · 23.5 mi · Higher grade (F → D)
Nearby Lakes in Wayne County
Explore Corydon Reservoir across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
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
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-09-09
Monitoring stations: 1