Skip to main content
LakeQuality
Pink and orange afterglow over the treeline on Slim Lake after sunset

Updated August 2026

The State of South Dakota's Lakes 2026

Of 8 lakes in South Dakota, 0% earn a water-quality grade of A or B and 100% score D or F (average grade F). Traverse Lake is the cleanest; 1 lakes (12.5%) are on an official impaired-waters list.

Data Report

8
Monitored lakes graded
F
Average grade
0%
Grade A or B
12.5%
On impaired list

South Dakota grade distribution

F
A: 0 (0.0%)B: 0 (0.0%)C: 0 (0.0%)D: 0 (0.0%)F: 2 (100.0%)

Cleanest lakes in South Dakota

Highest combined water-quality score, 2026.

  1. 1.FTraverse Lake — Roberts County3.9 ft clarity · 173 µg/L P · 36 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.FTraverse Lake — Roberts County3.9 ft clarity · 173 µg/L P · 36 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

  1. 1.FBig Stone Lake — Roberts County70 µg/L chlorophyll-a
  2. 2.FTraverse Lake — Roberts County36 µg/L chlorophyll-a

Trending lakes

Declining

  1. 1.FTraverse Lake — Roberts County

Impaired waters in South Dakota

1 lakes appear on the EPA/state 303(d) impaired-waters list (1 formally listed, 0 with a cleanup plan/TMDL).

Oxygen depletion (low DO) · 1pH / acidity · 1

Explore South Dakota lakes

Lake Fishing Forecast

Species activity outlook by water temperature and season

South Dakota Lake Trips

Where to stay at South Dakota's top lakes, each with its grade

Lakes near Sioux Falls

Best-graded lakes within 50 miles of Sioux Falls

Grades combine total phosphorus, total nitrogen, chlorophyll-a, and turbidity from the EPA Water Quality Portal and state agencies. See the full methodology, the national State of America’s Lakes report, or all South Dakota lakes.

Cite this report: LakeQuality, “The State of South Dakota's Lakes 2026”.