Nine Eagles Lake is a 59-acre mesotrophic lake in Decatur County, Iowa. Water quality is graded A based on 2 sampling years through 2024. Water clarity is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 2 other monitored lakes in Decatur County, Nine Eagles Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-15. Grade methodology: LakeGrade methodology.
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Swimming Safety
Based on E. coli testing, Nine Eagles Lake routinely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 28.2% of 110 samples across 7 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Iowa’s current beach and health-department advisories before swimming.
Water Quality Grade: A, Excellent
Good clarity, visible to about 11 ft. Chlorophyll-a: 3.3 µg/L. Trophic State Index: 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11 ft | B |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 3.3 µg/L | A |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 59 acres |
| Public Access | Yes |
Where to stay near Nine Eagles Lake
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Fishing Nine Eagles Lake
Water Quality Trend: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.162 m/yr | 4 |
| Chlorophyll-a | ↓ Declining | +1.23 µg/L/yr | 4 |
Recreation & Access
Water Temperature
Nine Eagles Lake averages about 81°F at the surface in summer, usually warmest in Jul (about 83°F) and coldest in May (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 111 field readings (2010–2023) via the EPA Water Quality Portal. See the full Nine Eagles Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Nine Eagles Lake, reaching a maximum surveyed depth of 30 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #1 of 3 lakes in Decatur County
Nearby Lakes in Decatur County
Explore Nine Eagles Lake across LakeGrade
More Iowa Lake Rankings
Other Grade A Lakes in Iowa
Mesotrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Nine Eagles Lake is a man-made reservoir impounded by the Nine Eagles Park Lake Dam (completed 1930), built primarily for recreation on the TR-THOMPSON RIVER; earth-type dam, 53 ft tall and 1,000 ft long.
- Surface area
- 59 ac
- Normal storage
- 840 ac-ft
- Max storage
- 1,560 ac-ft
- Drainage area
- 1.77 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA01340 · Operator website · Matched by proximity (0.12 km)
EPA Impairment Status
Nine Eagles Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 05-GRA-1361 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2024-09-15
Monitoring stations: 1