Sioux County Lake Quality
North Dakota, 1 lakes, average grade D (Poor)
Only 1 lakes in Sioux County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. On average, Sioux County lakes grade D, with phosphorus loading and reduced clarity showing up across most of the dataset.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Froelich Dam Lake (D) is the cleanest in the county.
Quick Answers for Sioux County
Planning a trip? Check special fishing regulations for Froelich Dam Lake, whether the fish are safe to eat, and the best times to fish — or check the official North Dakota fishing regulations.
All Lakes in Sioux County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Froelich Dam Lake | D | 3.9 ft | 34.2 ft | - |
Other Counties in North Dakota
See how Sioux County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 15 states.
Where to stay near Sioux County
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Source: EPA National Aquatic Resource Surveys, 2026.