Updated Aug 2026
South Dakota Lake Water Quality
Water quality grades for 9 monitored lakes across 5 counties.
9 South Dakota lakes carry a grade. Most of the input data flows through monitoring run by the South Dakota Department of Agriculture and Natural Resources, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. A-grade lakes are scarce in South Dakota: about 0% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
A meaningful share of the state's monitored lakes register as hypereutrophic — heavily nutrient-loaded, frequent blooms, low summer transparency. These are usually shallow, surrounded by row-crop agriculture, with little volume to buffer the inputs. Roberts ranks highest on average county grade (F). Roberts sits lowest. With only 5 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
All 9 South Dakota lakes in the index: 2 (22.2%) carry an A–F grade and 7 (77.8%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
Where to stay near South Dakota
Top-rated places to stay near South Dakota
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Top-Graded South Dakota Lakes
The highest water-quality grades in South Dakota — clarity, depth, and A-F grade at a glance.
Lake Map
Explore South Dakota Lakes
South Dakota reports, fishing & travel
Reservoirs in South Dakota
View all 1 reservoirs →1 of 9 South Dakota lakes (11%) are man-made reservoirs in the USACE National Inventory of Dams. 1 carry a High or Significant hazard rating. The oldest matched dam dates to 1976.
EPA-Impaired Lakes in South Dakota
View all 1 impaired lakes →1 of 9 South Dakota lakes (11%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle.
South Dakota Fishing & Recreation
Licenses, regulations, records, and where to fish across South Dakota.
Counties
All 5 South Dakota counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
South Dakota Lake Water Quality Dataset (2026)
Every graded South Dakota lake in one spreadsheet — A–F grade, water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's report card.
Cleanest South Dakota Lakes
2 lakes2 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Access |
|---|---|---|---|---|---|---|
| 1 | FBig Stone Lake | Roberts | F | 3 ft | Hypereutrophic | ✓ Public |
| 2 | FTraverse Lake | Roberts | F | 3.9 ft | Hypereutrophic | ✓ Public |
South Dakota Lakes Needing Attention
2 lakes2 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FTraverse Lake | Roberts | F | 3.9 ft |
| 2 | FBig Stone Lake | Roberts | F | 3 ft |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.
More on lake water quality
The top-graded lake in every state we cover, picked grade-first with water clarity as the tie-breaker — plus the states whose winner is still not clean.
State-by-state Secchi champions: the clearest measured lake in each U.S. state we grade, which is not the same as the cleanest nutrient grade.
A data snapshot of the lakes we grade: how the A–F distribution breaks down, the clearest and the greenest states, and where the water is improving.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.