What is the water quality grade for Green Valley Lake?

Green Valley Lake in Union County, Wisconsin received a water quality grade of F (Very Poor). Water clarity: 1.5 ft visibility. Chlorophyll-a (algae): 61.7 µg/L. Surface area: 336 acres.

Is Green Valley Lake safe to swim in?

Avoid swimming, very poor water quality, potential algae toxins. Green Valley Lake has an overall water quality grade of F. Algae concentration (chlorophyll-a) is 61.7 µg/L. Always check local health department advisories before swimming.

Green Valley Lake

Union County, WisconsinHypereutrophic

Green Valley Lake is a 336-acre highly nutrient-loaded hypereutrophic lake in Union County, IA. Water quality is graded F based on 2 sampling years through 2024. 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, local state DNR records, last sampled 2024-09-30. Grade methodology: LakeGrade methodology.

Swimming Safety

Avoid swimming, very poor water quality, potential algae toxins

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

Location

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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.

See full comparison →

Nearby Lakes in Union County

More Wisconsin Lake Rankings

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Top 25 by overall water quality score

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Grade A/B + low algae filter

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Other Grade F Lakes in Wisconsin

Big Creek Lake

Polk County · Clarity: 2.6 ft

Arrowhead Lake

Pottawattamie County · Clarity: 1.8 ft

White Oak Lake

Mahaska County · Clarity: 1.4 ft

Crystal Lake Max Depth

Hancock County · Clarity: 1.6 ft

Hannen Lake

Benton County · Clarity: 1.2 ft

Briggs Woods Lake

Hamilton County · Clarity: 1.5 ft

Hypereutrophic Lakes in Wisconsin

White Oak Lake Hannen Lake Briggs Woods Lake Union Grove Lake

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

Algal growthOxygen depletion (low DO)pH / acidityTurbidity

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit IA 05-PLA-1472 · Official waterbody report

Data Sources

Water quality data from the EPA Water Quality Portal

Impairment status from EPA ATTAINS 303(d) database

Grading methodology based on Metropolitan Council standards

Most recent sample: 2024-09-30

Monitoring stations: 1