Greenfield Lake is a 50-acre productive, nutrient-rich eutrophic lake in Adair 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 4 other monitored lakes in Adair County, Greenfield Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-29. Grade methodology: LakeGrade methodology.
Watch Greenfield Lake water quality
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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 2.1 ft of visibility. Chlorophyll-a: 53.8 µg/L. Trophic State Index: 68.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.1 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 53.8 µg/L | F |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 50 acres |
Where to stay near Greenfield Lake
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Fishing Greenfield Lake
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.009 m/yr | 5 |
| Chlorophyll-a | ↓ Declining | +2.9 µg/L/yr | 5 |
Water Temperature
Greenfield Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in Sep (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 29 field readings (2010–2023) via the EPA Water Quality Portal. See the full Greenfield Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Greenfield Lake, reaching a maximum surveyed depth of 24 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #3 of 5 lakes in Adair County
Cleaner Lakes Within 30 Miles
Greenfield Lake holds Grade F. 2 nearby lakes hold higher grades.
- CMormon Trail LakeAdair County · 8.9 mi · Two grade letters higher (F → C)
- DNodaway LakeAdair County · 1 mi · Higher grade (F → D)
Nearby Lakes in Adair County
Explore Greenfield Lake 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)
Greenfield Lake is a man-made reservoir impounded by the Greenfield Reservoir Dam (completed 1979), built primarily for water supply on the TR- MIDDLE NODAWAY R.; earth-type dam, 42 ft tall and 990 ft long.
- Surface area
- 49.6 ac
- Normal storage
- 612 ac-ft
- Max storage
- 1,150 ac-ft
- Drainage area
- 1.5 sq mi
- Hazard class
- High
- Owner
- Greenfield Municipal Utilities
Source: USACE National Inventory of Dams, NID ID IA02267 · Operator website
EPA Impairment Status
Greenfield Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit IA 05-NOD-1401 · Official waterbody report · Matched by proximity (1.55 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Greenfield Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger.
- Greenfield City Of StpGreenfield · 1.3 mi away · NPDES IA0021369Major
- Greenfield Municipal Utilities WtpGreenfield · 0.3 mi away · NPDES IA0048453
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: 2024-09-29
Monitoring stations: 1