Lagoon systems: wastewater treatment plants in Minnesota
327 plants · 70% of the state · 35 MGD reported by 65 plants
Klarifi identifies 327 publicly owned wastewater treatment plants with lagoon systems in Minnesota, 70% of the 470 plants in the state (35 MGD reported by 65 plants). The largest is Grand Rapids WWTP in Grand Rapids at 5.92 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 Minnesota
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Grand Rapids WWTP | Grand Rapids | 5.92 | MN0022080 | Jan 2025 | 7 |
| 2 | Moorhead Wastewater Treatment Facility | Moorhead | 3.8 | MN0049069 | Jun 2026 | 0 |
| 3 | Whitewater River Regional WWTP | Saint Charles | 2.35 | MN0046868 | Oct 2027 | 13 |
| 4 | Marshall WWTP | Marshall | 2.15 | MN0022179 | Feb 2029 | 16 |
| 5 | Saint Peter WWTP | Saint Peter | 1.46 | MN0022535 | Mar 2027 | 8 |
| 6 | Barnesville WWTP | Barnesville | 1.26 | MN0022501 | Apr 2026 | 98 |
| 7 | Rogers WWTP | Rogers | 1.16 | MN0029629 | Mar 2026 | 5 |
| 8 | Cold Spring WWTP | Cold Spring | 1.11 | MNL023094 | Dec 2030 | 0 |
| 9 | Long Prairie WWTP | Long Prairie | 1.1 | MN0066079 | Apr 2023 | 2 |
| 10 | Buffalo WWTP | Buffalo | 1.08 | MNL040649 | Dec 2030 | 1 |
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 Minnesota
Lagoon systems in other states
Lagoon systems in Minnesota: 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 October 26, 2026.
Wastewater terms: WWTP · POTW · Biosolids · Inflow and infiltration · Sludge dewatering · all terms