Green Valley Lake is a 336-acre highly nutrient-loaded hypereutrophic lake in Union County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 5 public boat landings. Compared to the 5 other monitored lakes in Union County, Green Valley Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-30. Grade methodology: LakeGrade methodology.
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Swimming Safety
Based on E. coli testing, Green Valley Lake rarely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 3.6% of 112 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: F, Very Poor
Very murky, less than 1.5 ft of visibility. Chlorophyll-a: 61.7 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 61.7 µg/L | F |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 336 acres |
| Public Access | Yes |
Where to stay near Green Valley Lake
Compare lakeside cabins, hotels, and vacation rentals near Green Valley Lake in Union 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.
Top-rated places to stay near Green Valley Lake
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Fishing Green Valley Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.026 m/yr | 5 |
| Chlorophyll-a | → Stable | +0.98 µg/L/yr | 5 |
Recreation & Access
Water Temperature
Green Valley Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in May (about 68°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 70 field readings (2011–2023) via the EPA Water Quality Portal. See the full Green Valley Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Green Valley Lake, reaching a maximum surveyed depth of 22 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #4 of 6 lakes in Union County
Cleaner Lakes Within 30 Miles
Green Valley Lake holds Grade F. 3 nearby lakes hold higher grades.
- CMormon Trail LakeAdair County · 16.5 mi · Two grade letters higher (F → C)
- DThree Mile LakeUnion County · 9.1 mi · Higher grade (F → D)
- DNodaway LakeAdair County · 14.5 mi · Higher grade (F → D)
Nearby Lakes in Union County
Explore Green Valley Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Green Valley Lake is a man-made reservoir impounded by the Green Valley Lake Dam (completed 1953), built primarily for recreation on the PLATTE RIVER; earth-type dam, 41 ft tall and 1,020 ft long.
- Surface area
- 336 ac
- Normal storage
- 3,990 ac-ft
- Max storage
- 6,830 ac-ft
- Drainage area
- 8.01 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IA01097 · Operator website
EPA Impairment Status
Green Valley 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-PLA-1472 · Official waterbody report
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 Green Valley Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Green Valley Chemical CorporationCreston · 1.9 mi away · NPDES IA0003964Recent violation
- Cipco - Summit LakeCreston · 2.2 mi away · NPDES IA0081442
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
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2024-09-30
Monitoring stations: 1