Green Valley Lake
Union County, Iowa336 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Green Valley Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Algal growth
- Public access
Green Valley Lake in Union County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 1.5 ft visibility. Phosphorus: 103 µg/L. Chlorophyll-a (algae): 61.7 µg/L. Surface area: 336 acres.
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. 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. Methodology: how these readings are compared.
Green Valley Lake covers about 340 acres in Union County. It has 2 public boat landings, so a lakefront rental is not the only way to get a boat on the water. Vrbo is where to look for cabins and lake homes around Green Valley Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Green Valley Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
Swimming conditions
Readings onlyRecreation use not supported
Based on clarity and algae readings from past sampling — there is no 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.
Whether Green Valley Lake is safe to swim in today is a call for the Iowa Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Green Valley Lake
These are the measurements Iowa DNR publishes for Green Valley Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.5 ft of visibility. Phosphorus 103 µg/L. Chlorophyll-a 61.7 µg/L. TSI 71.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 103µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 61.7µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 71 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Green Valley Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (68°F) to its warmest (81°F).
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
Surface area
336 acres
Public access
Yes
Listed by Iowa DNR
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
Stays via Stay22
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 readings cover nutrients and algae, not lodging. Cabins and rentals around Green Valley Lake are listed below.
Top-rated places to stay near Green Valley Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Green Valley Lake → · more Iowa lake trips
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Fishing Green Valley Lake
Water Quality Trend: Improving
Based on 5 years of monitoring (2020–2024).
Water clarity
Improving5 years
Phosphorus
Improving-27.1 µg/L/yr4 years
Chlorophyll-a
Stable+0.98 µg/L/yr5 years
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
Designated uses not supporting: Drinking water, Aquatic life, Recreation.
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.
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. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Green Valley Lake?
- Green Valley Lake in Union County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. 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 is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Green Valley Lake is safe to swim in today is a call for Iowa's water agency and the county health department; check their current beach 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.
Can I fish at Green Valley Lake?
- Green Valley Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Iowa's fish and wildlife agency, so check its current regulations before you go.
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 readings
Iowa's cleanest lakes, ranked on agency measurements
More lakes in Iowa
Other Lakes in Iowa
Hypereutrophic Lakes in Iowa
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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from 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