Lagoon systems: wastewater treatment plants in Iowa
632 plants · 93% of the state · 2 MGD reported by 8 plants
Klarifi identifies 632 publicly owned wastewater treatment plants with lagoon systems in Iowa, 93% of the 678 plants in the state (2 MGD reported by 8 plants). The largest is Walnut City Of STP in Walnut at 0.99 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 Iowa
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Walnut City Of STP | Walnut | 0.99 | IA0042986 | Apr 2006 | 40 |
| 2 | Clarion, City Of STP | Clarion | 0.82 | IA0030945 | Jan 2028 | 13 |
| 3 | Fredricksburg WWTP | Fredericksburg | 0.17 | IA0028991 | Jan 2008 | 0 |
| 4 | Ossian City Of STP | Ossian | 0.07 | IA0042781 | Sep 2006 | 5 |
| 5 | What Cheer WWTP | What Cheer | 0.04 | IA0032468 | Apr 2006 | 3 |
| 6 | Lester City Of STP | Lester | 0.04 | IA0026620 | Feb 2017 | 15 |
| 7 | Birmingham City Of STP | Birmingham | 0.04 | IA0023426 | Jul 2002 | 16 |
| 8 | Mitchell County WW Pretreatment Plant | Osage | 0.03 | MO0030821 | Jun 2026 | 111 |
| 9 | Ackley WWTP | Ackley | — | IA0035297 | May 2030 | 95 |
| 10 | Adel WWTP | Adel | — | IA0041921 | Nov 2027 | 2 |
| 11 | Afton City Of STP | Afton | — | IA0041831 | Jun 2027 | 0 |
| 12 | Agncy City Of STP | Agency | — | IA0057754 | Aug 2006 | 15 |
| 13 | Ainsworth City Of STP | Ainsworth | — | IA0069183 | Apr 2027 | 13 |
| 14 | Akron City Of STP | Akron | — | IA0035211 | Aug 2028 | 4 |
| 15 | Albia City Of STP (north) | Albia | — | IA0036871 | Apr 2026 | 62 |
| 16 | Albion City Of STP | Albion | — | IA0034321 | Apr 2030 | 29 |
| 17 | Alburnett WWTP | Alburnett | — | IA0024431 | Sep 2030 | 10 |
| 18 | Alden WWTP | Alden | — | IA0034339 | Aug 2030 | 4 |
| 19 | Allerton City Of STP North | Allerton | — | IA0054054 | Aug 2026 | 6 |
| 20 | Allerton City Of STP South | Allerton | — | IA0054046 | Aug 2026 | 34 |
| 21 | Allison City Of STP | Allison | — | IA0042731 | Aug 2030 | 42 |
| 22 | Alvord City Of STP | Alvord | — | IA0059722 | Nov 2019 | 4 |
| 23 | Amana Sanitary District | Amana | — | IA0059161 | Jul 2021 | 0 |
| 24 | Andover City Of STP | Andover | — | IA0021091 | May 2029 | 10 |
| 25 | Andrew WWTP | Andrew | — | IA0057975 | Aug 2016 | 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 Iowa
Lagoon systems in other states
Lagoon systems in Iowa: 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.