Green Valley Lake
Union County, Iowa336 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Algal growth
- #3 of 6 in the county
- Public access
Green Valley Lake in Union County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.5 ft visibility. Phosphorus: 103 µg/L. Chlorophyll-a (algae): 61.7 µg/L. Surface area: 336 acres.
- Clarity
- 1.5 ft
- Typical in September
- 70°F
- Area
- 336 acres
- Type
- Hypereutrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Stays 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Green Valley Lake are listed below.
Top-rated places to stay near Green Valley Lake
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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.
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 2 public boat landings. Compared to the 5 other monitored lakes in Union County, Green Valley Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-30. Grade methodology: LakeQuality methodology.
What Green Valley Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
Swimming Safety
Grade onlyBacteria A
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.
Based on E. coli testing, Green Valley Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 7 samples across 3 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 (Algae-prone)
Very murky, less than 1.5 ft of visibility. Phosphorus 103 µg/L. Chlorophyll-a 61.7 µg/L. TSI 71. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | Not graded |
| Phosphorus | 103 µg/L | Poor |
| Chlorophyll-a (Algae) | 61.7 µg/L | Poor |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Green Valley Lake typically sits around 70°F at the surface in September. Summer average is about 78°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 336 acres |
| Public Access | Yes |
No bathymetric survey has been published for Green Valley Lake, so its depth is not documented here.
Recreation & Access
- Summit Lake - City of CrestonPublic
- Green Valley State ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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 |
| Phosphorus | ↑ Improving | -27.1 µg/L/yr | 4 |
| Chlorophyll-a | → Stable | +0.98 µg/L/yr | 5 |
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
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.
County Ranking
Ranked #3 of 6 lakes in Union County
Nearby Lakes With Higher Grades
Green Valley Lake holds Grade F. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Union County
Frequently asked questions about Green Valley Lake
Where is Green Valley Lake?
- Green Valley Lake is a lake in Union County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Green Valley Lake?
- Green Valley Lake in Union County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.5 ft visibility. Phosphorus: 103 µg/L. Chlorophyll-a (algae): 61.7 µg/L. Surface area: 336 acres.
Is Green Valley Lake safe to swim in?
- Based on E. coli testing, Green Valley Lake never exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 0% of 7 samples across 3 seasons. That works out to a bacteria swim-safety grade of A — a historical summary of past testing, not a current reading. Green Valley Lake has a water quality grade of F (Algae-prone). Bacteria levels can spike quickly after heavy rain, so always check Iowa's current beach and health-department advisories before you swim.
What is the water temperature of Green Valley Lake?
- Green Valley Lake typically sits around 70°F at the surface in September, from 70 EPA Water Quality Portal field readings (2011–2023). That is a typical value for the month, not a live reading.
Are there boat ramps on Green Valley Lake?
- Green Valley Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Summit Lake - City of Creston, Green Valley State Park. Public access is listed as yes.
Explore Green Valley Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Iowa's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
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Other Grade F Lakes in Iowa
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Where this data comes from
60 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX60 samples · 2020–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 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)
Named boat-access points from the USGS National Boat Ramps inventory