Green Castle Lake
Marshall County, WisconsinEutrophic
Green Castle Lake is a 17-acre productive, nutrient-rich eutrophic lake in Marshall County, IA. Water quality is graded C based on 2 sampling years through 2024. Compared to the 1 other monitored lakes in Marshall County, Green Castle Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-08-25. Grade methodology: LakeGrade methodology.
Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 4.6 ft. Chlorophyll-a: 6.9 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.6 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 6.9 µg/L | B |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 17 acres |
Location
County Ranking
Ranked #2 of 2 lakes in Marshall County
Cleaner Lakes Within 30 Miles
Green Castle Lake holds Grade C. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Marshall County
More Wisconsin Lake Rankings
Other Grade C Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Reservoir Info (USACE NID)
Green Castle Lake is a man-made reservoir impounded by the Green Castle Dam (completed 1954), built primarily for recreation on the TR- BRUSH CREEK; earth-type dam, 30 ft tall and 650 ft long.
- Surface area
- 17 ac
- Normal storage
- 150 ac-ft
- Max storage
- 263 ac-ft
- Drainage area
- 0.44 sq mi
- Hazard class
- Significant
- Owner
- Marshall County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA02418 · Operator website
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-08-25
Monitoring stations: 1