Marshall County Lake Quality
Wisconsin, 2 lakes, average grade C (Fair)
Marshall County has 2 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. Marshall County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.
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. Sand Lake (B) is the cleanest in the county.
Quick Answers for Marshall County
Planning a trip? Check special fishing regulations for Sand Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Marshall County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Sand Lake | B | 6.4 ft | - | - |
| 2 | Green Castle Lake | C | 4.6 ft | - | - |
Source: EPA National Aquatic Resource Surveys, 2026.