Lagoon systems: wastewater treatment plants in California
110 plants · 57% of the state · 193 MGD reported by 57 plants
Klarifi identifies 110 publicly owned wastewater treatment plants with lagoon systems in California, 57% of the 193 plants in the state (193 MGD reported by 57 plants). The largest is Stockton Rwcf in Stockton at 29.2 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 California
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Stockton Rwcf | Stockton | 29.2 | CA0079138 | Jul 2030 | 57 |
| 2 | Riverside City, Water Quality Control | Riverside | 27.72 | CA0105350 | Oct 2018 | 2 |
| 3 | Colton/san Bernardino Stp, Rix | Colton | 21.06 | CA8000304 | Jul 2018 | 0 |
| 4 | Victor Valley Wastewater Reclamation Authority | Victorville | 9.48 | CA0102822 | May 2025 | 7 |
| 5 | Hill Canyon WWTP | Camarillo | 8.09 | CA0056294 | Jul 2031 | 3 |
| 6 | Corona WWTP 1 | Corona | 7.64 | CA8000383 | Jun 2025 | 9 |
| 7 | Michelson Treatment Plant | Irvine | 6.99 | CA8000326 | Jun 2020 | 16 |
| 8 | Simi Vly Cnty Sanitation | Simi Valley | 6.5 | CA0055221 | Jul 2031 | 37 |
| 9 | Clear Creek WWTP | Anderson | 5.67 | CA0079731 | Jul 2027 | 16 |
| 10 | Manteca Wwqcf | Manteca | 5.18 | CA0081558 | Mar 2026 | 7 |
| 11 | Yuba City Wastewater Treatment Facility | Yuba City | 5.05 | CA0079260 | Mar 2024 | 21 |
| 12 | Water Reclamation Plant No. 4 | Thermal | 4.93 | CA0104973 | Apr 2028 | 11 |
| 13 | San Luis Obispo WWTP | San Luis Obispo | 4.23 | CAL049224 | Dec 2030 | 23 |
| 14 | El Centro WWTP | El Centro | 3.7 | CA0104426 | Mar 2024 | 17 |
| 15 | Camarillo Sanitary Dist Water Reclamation Plant | Camarillo | 3.57 | CA0053597 | Dec 2024 | 88 |
| 16 | Sewerage Commission - Oroville Region | Oroville | 3.4 | CA0079235 | Sep 2026 | 0 |
| 17 | Davis Water Pollution Control Plant | Davis | 3.2 | CA0079049 | Jul 2030 | 41 |
| 18 | Eureka Wastewater Treatment Plant | Eureka | 3.08 | CA0024449 | Oct 2028 | 24 |
| 19 | Woodland WPCF | Woodland | 2.61 | CA0077950 | Mar 2030 | 2 |
| 20 | Calexico Waste Water Plant | Calexico | 2.5 | CA7000009 | May 2024 | 9 |
| 21 | Linda County WWTP | Marysville | 2.41 | CA0079651 | Jan 2028 | 21 |
| 22 | Redding Stillwater Wastewater Treatment Plant | Anderson | 2.32 | CA0082589 | May 2028 | 6 |
| 23 | City Of Paso Robles Wastewater Treatment Facility | Paso Robles | 2.27 | CA0047953 | Jun 2026 | 17 |
| 24 | Olivehurst WWTF | Olivehurst | 1.99 | CA0077836 | May 2026 | 24 |
| 25 | Merced WWTF | Merced | 1.87 | CA0079219 | May 2025 | 5 |
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 California
Lagoon systems in other states
Lagoon systems in California: 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.