Lagoon systems: wastewater treatment plants in Wisconsin
161 plants · 41% of the state · 41 MGD reported by 117 plants
Klarifi identifies 161 publicly owned wastewater treatment plants with lagoon systems in Wisconsin, 41% of the 391 plants in the state (41 MGD reported by 117 plants). The largest is Appleton City WWTF in Appleton at 9.25 MGD.
Lagoon systems treat wastewater in large earthen ponds over weeks of retention time, with or without mechanical aeration. They serve thousands of small towns because they are cheap to run, but they struggle with ammonia and nutrient limits, fill with sludge over decades and are the plants most often converted or upgraded when a permit is renewed.
The largest lagoons in Wisconsin
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Appleton City WWTF | Appleton | 9.25 | WI0023221 | Mar 2022 | 7 |
| 2 | Fox River Water Pollution Control Center | Brookfield | 8.95 | WI0023469 | Dec 2023 | 10 |
| 3 | Rib Mountain Sewage Dist | Wausau | 2.94 | WI0035581 | Dec 2023 | 3 |
| 4 | Portage Wastewater Treatment Facility | Portage | 1.52 | WI0020427 | Sep 2021 | 32 |
| 5 | Monroe Wastewater Treatment Facility | Monroe | 1.5 | WI0020362 | Dec 2025 | 17 |
| 6 | Arcadia Wastewater Treatment F | Arcadia | 1.19 | WI0023230 | Jun 2025 | 1 |
| 7 | Fontana-Walworth Water Pollution Control Commission | Fontana | 0.9 | WI0036021 | Dec 2023 | 21 |
| 8 | Ashland Sewage Utility | Ashland | 0.85 | WI0030767 | Mar 2022 | 1 |
| 9 | Dodgeville Wastewater Treatment Facility | Dodgeville | 0.72 | WI0026913 | Dec 2025 | 0 |
| 10 | Green Lake Sanitary District | Princeton | 0.69 | WI0036846 | Sep 2022 | 18 |
| 11 | Whitehall Wastewater Treatment Facility | Whitehall | 0.65 | WI0030970 | Sep 2024 | 9 |
| 12 | Stanley Wastewater Treatment Facility | Stanley | 0.53 | WI0021857 | Sep 2023 | 33 |
| 13 | Consolidated Koshkonong Sanitary District Site | Edgerton | 0.49 | WI0021059 | Sep 2023 | 0 |
| 14 | Edgerton Wastewater Treatment Facility | Edgerton | 0.47 | WI0020346 | Sep 2023 | 16 |
| 15 | Tomahawk Waterworks | Tomahawk | 0.39 | WI0021946 | Dec 2023 | 3 |
| 16 | Thorp Wastewater Treatment Facility | Thorp | 0.36 | WI0025615 | Jun 2023 | 38 |
| 17 | Black Creek Wastewater Treatme | Black Creek | 0.34 | WI0021041 | Jun 2013 | 16 |
| 18 | Rio Wastewater Treatment Facility | Rio | 0.34 | WI0020117 | Sep 2023 | 2 |
| 19 | Park Falls City Of | Park Falls | 0.32 | WI0029033 | Sep 2020 | 16 |
| 20 | New Lisbon Wastewater Treatment Facility | New Lisbon | 0.31 | WI0020699 | Sep 2019 | 0 |
| 21 | Ladysmith City Of | Ladysmith | 0.3 | WI0021326 | Mar 2022 | 1 |
| 22 | Freedom Sanitary District #1 | Kaukauna | 0.28 | WI0020842 | Dec 2021 | 2 |
| 23 | Owen Wastewater Treatment Facility | Owen | 0.28 | WI0020940 | Jun 2023 | 1 |
| 24 | Holland Sd 1 Wastewater Trtmnt | Holland | 0.25 | WI0028207 | Dec 2023 | 0 |
| 25 | Port Edwards Wastewater Treatment Facility | Port Edwards | 0.23 | WI0020451 | Sep 2020 | 0 |
Contacts and project signals for every plant on this list
Klarifi adds verified decision-maker contacts, permit limits, discharge monitoring data and the capital projects planned in each city, filterable by technology, size and compliance record.
Other technologies in Wisconsin
Lagoon systems in other states
Lagoon systems in Wisconsin: questions
Sources and methodology
Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.
Data refreshed September 11, 2026.