How Clean Is Green Castle Lake?
Green Castle Lake has fair water quality — typical of lakes with moderate nutrient enrichment. It received a water quality grade of C (Fair) based on EPA monitoring data. Water clarity (Secchi depth): 4.6 ft. Chlorophyll-a (algae): 6.9 µg/L. Trophic State Index: 52.
Cleanliness Snapshot
| Metric | Green Castle Lake | Wisconsin avg |
|---|---|---|
| Overall Grade | C | D |
| Water Clarity (Secchi) | 4.6 ft | — |
| Chlorophyll-a (Algae) | 6.9 µg/L | <10 = clean |
| Trophic State Index | 52 | <50 = clean |
How does Green Castle Lake compare?
Green Castle Lake's grade of C matches or beats the Wisconsin state average of D. It ranks #2 of 2 lakes in Marshall County by water quality score.