Wisconsin Lake Water Quality
Water quality grades for 54 monitored lakes across 8 counties.
A-grade lakes are scarce in Pennsylvania: about 2% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
The state's lakes lean eutrophic: enough nutrient input to support an active algal community, with the trade-offs in clarity and dissolved oxygen that come with it. Erie ranks highest on average county grade (A). Pike sits lowest. With only 8 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Lake Map
Reservoirs in Wisconsin
View all 11 reservoirs →11 of 54 Wisconsin lakes (20%) are man-made reservoirs in the USACE National Inventory of Dams. 5 carry a High or Significant hazard rating. The oldest matched dam dates to 1876.
EPA-Impaired Lakes in Wisconsin
View all 16 impaired lakes →16 of 54 Wisconsin lakes (30%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 3 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Counties
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity | Max Depth |
|---|---|---|---|---|---|
| 1 | Er63 Lake | Erie | A | 16.4 ft | - |
| 2 | Susq 44b Lake | Lancaster | B | - | - |
| 3 | Susq 65a Lake | Dauphin | B | - | - |
| 4 | Susq 34a Lake | Lancaster | B | - | - |
| 5 | Susq 65b Lake | Dauphin | B | - | - |
| 6 | Susq 69b Lake | Dauphin | B | - | - |
| 7 | Susq 61a Lake | Dauphin | B | - | - |
| 8 | Susq 61b Lake | Dauphin | B | - | - |
| 9 | Susq 22b Lake | Lancaster | C | - | - |
| 10 | Susq 47b Lake | Lancaster | C | - | - |
| 11 | Susq 18b Lake | Lancaster | C | - | - |
| 12 | Susq 58c Lake | Dauphin | C | - | - |
| 13 | Susq 65c Lake | Dauphin | C | - | - |
| 14 | Susq 38b Lake | Lancaster | C | - | - |
| 15 | Susq 18a Lake | Lancaster | C | - | - |
| 16 | Susq 58b Lake | Dauphin | C | - | - |
| 17 | Susq 44a Lake | Lancaster | C | - | - |
| 18 | Susq 30b Lake | Lancaster | C | - | - |
| 19 | Susq 44c Lake | Lancaster | C | - | - |
| 20 | Susq 30a Lake | Lancaster | C | - | - |
| 21 | Susq 53b Lake | Lancaster | C | - | - |
| 22 | Susq 58a Lake | Dauphin | C | - | - |
| 23 | Susq 22c Lake | Lancaster | C | - | - |
| 24 | Susq 18c Lake | Lancaster | C | - | - |
| 25 | Susq 47c Lake | Lancaster | C | - | - |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Susq 47a Lake | Lancaster | F | - |
| 2 | Oct20 Lake | Chester | D | - |
| 3 | Oct10 Lake | Lancaster | D | - |
| 4 | 1h Lake | Lancaster | D | - |
| 5 | 1a Lake | Lancaster | D | - |
| 6 | Octr 0.0 Lake | Lancaster | D | - |
| 7 | Octr 2.0 Lake | Lancaster | D | - |
| 8 | Octr 1.0 Lake | Lancaster | D | - |
| 9 | Susq 53a Lake | Lancaster | D | - |
| 10 | Susq 53c Lake | Lancaster | D | - |
| 11 | Susq 26a Lake | Lancaster | D | - |
| 12 | Susq 26b Lake | Lancaster | D | - |
| 13 | Susq 38a Lake | Lancaster | D | - |
| 14 | Susq 34b Lake | Lancaster | D | - |
| 15 | Susq 34c Lake | Lancaster | D | - |
| 16 | Susq 30c Lake | Lancaster | D | - |
| 17 | Susq 26c Lake | Lancaster | D | - |
| 18 | Susq 38c Lake | Lancaster | D | - |
| 19 | Lake Nockamixon | Bucks | D | 4.8 ft |
| 20 | Lake Carey | Wyoming | D | 5.9 ft |
| 21 | Lake Wallenpaupack | Pike | D | 5.7 ft |
| 22 | Oct16 Lake | Lancaster | C | - |
| 23 | 1f Lake | Lancaster | C | - |
| 24 | 1j Lake | Lancaster | C | - |
| 25 | 1c Lake | Lancaster | C | - |
Source: EPA National Aquatic Resource Surveys, 2026.