Lagoon systems: wastewater treatment plants in Louisiana
77 plants · 30% of the state · 53 MGD reported by 66 plants
Klarifi identifies 77 publicly owned wastewater treatment plants with lagoon systems in Louisiana, 30% of the 259 plants in the state (53 MGD reported by 66 plants). The largest is Monroe, City Of (wpc Cntr) in Monroe at 6.09 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 Louisiana
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Monroe, City Of (wpc Cntr) | Monroe | 6.09 | LAL038741 | Dec 2030 | 78 |
| 2 | Hammond North STP | Hammond | 4.87 | LA0032328 | Aug 2028 | 36 |
| 3 | Carrollton Water Purification Plant | New Orleans | 3.38 | LA0000086 | Jun 2025 | 53 |
| 4 | Shreveport North Regional WWTP | Shreveport | 2.71 | LAL042188 | Dec 2030 | 42 |
| 5 | Wards 5 & 8 Joint Sewerage Commision | Patterson | 2.55 | LA0068381 | Sep 2030 | 99 |
| 6 | Denham Springs Wastewater Treatment Facility | Denham Springs | 2.39 | LAL045730 | Dec 2030 | 207 |
| 7 | Thibodaux, City Of- Wastewater Treatment Facility | Thibodaux | 2.1 | LA0032948 | Jul 2029 | 77 |
| 8 | Broussard, City Of | Broussard | 1.68 | LA0020613 | Apr 2031 | 19 |
| 9 | Jennings, City Of- WWTP | Jennings | 1.61 | LA0041769 | Oct 2025 | 16 |
| 10 | St. Charles Parish Council | Hahnville | 1.43 | LAL073521 | Dec 2030 | 2 |
| 11 | Donaldsonville, City Of | Donaldsonville | 1.34 | LA0043931 | Mar 2029 | 18 |
| 12 | Breaux Bridge Wastewater Treatment Plant | Breaux Bridge | 1.32 | LA0033014 | Sep 2027 | 31 |
| 13 | Sewerage District #1 Of Iberia Parish & City Of New Iberia- Tete Bayou WWTP | New Iberia | 1.27 | LA0065251 | Apr 2027 | 108 |
| 14 | Ponchatoula, City Of- Wastewater Treatment Facility | Ponchatoula | 1.24 | LA0044695 | Jan 2031 | 131 |
| 15 | Gretna City Of Wastewater Treatment Plant | Gretna | 1.17 | LA0041262 | Aug 2028 | 10 |
| 16 | Youngsville Wastewater Treatment Facility | Youngsville | 1.17 | LA0055328 | Apr 2018 | 32 |
| 17 | Lafayette Consolidated Government - Northeast WWTP | Lafayette | 1.16 | LAL036391 | Dec 2030 | 0 |
| 18 | Natchitoches, City Of | Natchitoches | 1.13 | LAL095222 | Dec 2030 | 23 |
| 19 | Delhi, Town Of - WWTP | Delhi | 1.1 | LA0039802 | Nov 2027 | 104 |
| 20 | Crowley WWTP | Crowley | 1.1 | LA0041254 | Oct 2030 | 43 |
| 21 | Oakdale, City Of | Oakdale | 1.07 | LA0033430 | Jul 2029 | 90 |
| 22 | Rayville WWTF | Rayville | 1.05 | LA0020559 | May 2028 | 180 |
| 23 | Luling Oxidation Pond | Luling | 0.84 | LA0032131 | May 2028 | 7 |
| 24 | Leesville, City Of | Leesville | 0.81 | LA0043575 | Aug 2028 | 124 |
| 25 | Scott Wastewater Treatment Facility | Scott | 0.77 | LA0034495 | Aug 2028 | 181 |
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 Louisiana
Lagoon systems in other states
Lagoon systems in Louisiana: 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.