What is the water quality grade for Black Hawk Lake?

Black Hawk Lake in Sac County, Wisconsin received a water quality grade of F (Very Poor). Water clarity: 0.9 ft visibility. Chlorophyll-a (algae): 54.1 µg/L. Surface area: 920 acres.

Is Black Hawk Lake safe to swim in?

Avoid swimming, very poor water quality, potential algae toxins. Black Hawk Lake has an overall water quality grade of F. Algae concentration (chlorophyll-a) is 54.1 µg/L. Always check local health department advisories before swimming.

Black Hawk Lake

Sac County, WisconsinHypereutrophic

Black Hawk Lake is a 920-acre highly nutrient-loaded hypereutrophic lake in Sac County, IA. Water quality is graded F based on 2 sampling years through 2024. Compared to the 1 other monitored lakes in Sac County, Black Hawk Lake ranks #2 for water quality.

Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-09-04. 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 0.9 ft of visibility. Chlorophyll-a: 54.1 µg/L. Trophic State Index: 74.

Metric	Value	Grade
Water Clarity (Secchi Depth)	0.9 ft	F
Phosphorus	No data
Chlorophyll-a (Algae)	54.1 µg/L	F
Trophic State Index (TSI)	74	Hypereutrophic

Very high nutrients, dense algae, poor clarity

Lake Details

Characteristic	Value
Surface Area	920 acres

Location

Loading map…

County Ranking

Ranked #2 of 2 lakes in Sac County

Cleaner Lakes Within 30 Miles

Black Hawk Lake holds Grade F. 5 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Sac County

More Wisconsin Lake Rankings

Cleanest lakes in Wisconsin

Top 25 by overall water quality score

Best swimming lakes in Wisconsin

Grade A/B + low algae filter

Family fishing lakes in Wisconsin

Panfish-rich, public access

All Wisconsin lakes

Full state directory

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)

Black Hawk Lake is a man-made reservoir impounded by the Black Hawk Lake Dam (completed 1916), built primarily for flood risk reduction on the Wall Lake Outlet; earth-type dam, 12 ft tall.

Surface area: 920 ac
Normal storage: 5,520 ac-ft
Max storage: 10,500 ac-ft
Drainage area: 23.4 sq mi
Hazard class: Significant
Owner: Iowa Department of Natural Resources

All listed purposes: Flood Risk Reduction;Other;Recreation.

Source: USACE National Inventory of Dams, NID ID IA03524 · Operator website

EPA Impairment Status

Black Hawk 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 growthPathogens (E. coli, fecal)Turbidity

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

Source: EPA ATTAINS assessment unit IA 04-RAC-1134 · 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: 2024-09-04

Monitoring stations: 1