Lakes / South Dakota / Brookings County / Mortimer Slough
Mortimer Slough, South Dakota
138.63 acres
Surface Area
Where It Sits, and How Deep It Goes
Locator - South Dakota
44.46 degrees N, 97.00 degrees W - Brookings County. State and county outlines drawn from Census boundary data; the lake marker is placed by its USGS National Hydrography Dataset coordinates, not by eye. Schematic - not a survey map.
How Mortimer Slough Stacks Up
- Larger than 52% of the 533 lakes counted in South Dakota.
- About 31 miles from Watertown, as the crow flies.
Lakes Nearby
| Lake | County | Distance | Surface Area |
|---|---|---|---|
| Lake Tetonkaha | Brookings | 1.0 mi | 1,126.56 acres |
| Moe Slough | Brookings | 1.6 mi | 104.03 acres |
| Lake Oakwood | Brookings | 2.0 mi | 866.35 acres |
| Lake Mitchell | Brookings | 5.3 mi | 199.41 acres |
| Lake Thisted | Kingsbury | 7.8 mi | 272.8 acres |
| Lake Goldsmith | Brookings | 8.1 mi | 289.85 acres |
Straight-line distance between lake centers.
Facts and Figures
Questions About Mortimer Slough
How Big Is Mortimer Slough?
Mortimer Slough covers 138.63 acres in Brookings County, South Dakota.
What Is the Largest Lake in Brookings County?
Lake Sinai is the largest lake in Brookings County, at 1,789.59 acres.
Largest Lakes in South Dakota
| # | Lake | County | Surface Area | Max Depth |
|---|---|---|---|---|
| 1 | Lake Oahe | Dewey | 309,912.57 acres | - |
| 2 | Lake Francis Case | Charles Mix | 82,166.92 acres | - |
| 3 | Lake Sharpe | Hughes | 58,419.67 acres | - |
| 4 | Lewis and Clark Lake | Bon Homme | 25,141.99 acres | - |
| 5 | Lake Thompson | Kingsbury | 13,887.93 acres | - |
All 533 South Dakota lakes ranked by surface area
Sources: USGS National Hydrography Dataset (The National Map) lake data (ID 126759114). Verified October 30, 2026.