The 50 largest wastewater treatment plants in Idaho
Ranked by average flow · 106 MGD combined · 98% of the state's reported flow
West Boise WWTP in Garden City is the largest publicly owned wastewater treatment plant in Idaho by reported average flow, treating about 50.91 million gallons per day. The 50 plants below treat 106 MGD between them, 98% of the flow reported by all 94 plants in the state, and serve about 839,411 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.
| # | Facility | City | Avg flow (MGD) | Population | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|---|
| 1 | West Boise WWTP | Garden City | 50.91 | 380,979 | ID0023981 | Jun 2027 | 10 |
| 2 | Nampa WWTP | Nampa | 10.69 | 100,200 | ID0022063 | Oct 2021 | 27 |
| 3 | Pocatello City WWTP | Pocatello | 6.38 | 72,392 | ID0021784 | Aug 2017 | 8 |
| 4 | Lewiston WWTP | Lewiston | 3.36 | 45,845 | ID0022055 | Jan 2021 | 0 |
| 5 | Jerome WWTP | Jerome | 3.33 | 12,641 | ID0020168 | Jun 2015 | 4 |
| 6 | Rexburg WWTP | Rexburg | 3.22 | 2,602 | ID0023817 | Mar 2028 | 41 |
| 7 | St Maries WWTP | Saint Maries | 2.25 | 3,182 | ID0022799 | Oct 2025 | 36 |
| 8 | Page WWTP | Smelterville | 2.04 | 17,263 | ID0021300 | Sep 2018 | 1 |
| 9 | Moscow STP | Moscow | 1.84 | 25,702 | ID0021491 | Jan 2031 | 0 |
| 10 | Oxbow WWTP | Shelley | 1.82 | 39,474 | ID0020133 | May 2019 | 0 |
| 11 | Emmett WWTP | Emmett | 1.68 | 7,647 | ID0020311 | Jan 2007 | 2 |
| 12 | Star WWTP | Star | 1.52 | — | ID0023591 | Apr 2020 | 0 |
| 13 | Kuna North WWTP | Meridian | 1.3 | 29,000 | ID0028355 | May 2014 | 5 |
| 14 | Hayden Area Regional Sewer Board WWTP | Hayden | 1.24 | 17,178 | ID0026590 | May 2029 | 5 |
| 15 | Ketchum Sun Valley WWTP | Ketchum | 1.14 | 5,338 | ID0020281 | Jul 2017 | 0 |
| 16 | Salmon Sewage Lagoon | Salmon | 1.09 | 3,119 | ID0020001 | May 2026 | 2 |
| 17 | Soda Springs WWTP | Soda Springs | 0.93 | 3,084 | ID0020818 | Jun 2025 | 1 |
| 18 | New Meadows WWTP | New Meadows | 0.92 | 517 | ID0023159 | Jul 2018 | 13 |
| 19 | Weiser WWTP | Weiser | 0.87 | 5,500 | ID0020290 | Dec 2016 | 0 |
| 20 | Payette WWTP | Payette | 0.84 | 8,415 | ID0020672 | Oct 2019 | 1 |
| 21 | Fruitland Payette River WWTP | Payette | 0.7 | — | ID0021199 | Oct 2016 | 3 |
| 22 | Rigby WWTP | Rigby | 0.68 | 4,117 | ID0020010 | Dec 2021 | 9 |
| 23 | Montpelier WWTF | Montpelier | 0.49 | 2,643 | ID0025585 | Feb 2025 | 5 |
| 24 | American Falls WWTP | American Falls | 0.48 | 5,243 | ID0020753 | Jul 2019 | 2 |
| 25 | Heyburn WWTP | Heyburn | 0.43 | 3,592 | ID0020940 | Jan 2007 | 17 |
| 26 | Grangeville WWTP | Grangeville | 0.42 | 3,187 | ID0020036 | Apr 2025 | 3 |
| 27 | Kootenai-Ponderay WWTP | Sandpoint | 0.38 | 2,792 | ID0021229 | Aug 2023 | 2 |
| 28 | Driggs WWTP | Driggs | 0.37 | 4,169 | ID0020141 | Dec 2015 | 167 |
| 29 | Council WWTP | Council | 0.33 | 867 | ID0020087 | Aug 2025 | 3 |
| 30 | Genesee, City Of - Genesee WWTP | Genesee | 0.3 | — | ID0030112 | Oct 2030 | 0 |
| 31 | Craigmont WWTP | Craigmont | 0.3 | 510 | ID0021288 | May 2025 | 49 |
| 32 | Riverside Water And Sewer District WWTP | Orofino | 0.28 | 2,117 | ID0024503 | Dec 2026 | 4 |
| 33 | Bonners Ferry WWTP | Bonners Ferry | 0.28 | 2,520 | ID0020222 | Oct 2016 | 1 |
| 34 | Buhl WWTP | Buhl | 0.28 | 4,558 | ID0020664 | Oct 2012 | 2 |
| 35 | Weippe WWTP | Weippe | 0.27 | 450 | ID0020354 | Oct 2019 | 6 |
| 36 | St Anthony Sewage Lagoon | Saint Anthony | 0.26 | 4,525 | ID0020401 | Nov 2014 | 7 |
| 37 | Homedale WWTP | Homedale | 0.25 | 2,881 | ID0020427 | Sep 2018 | 18 |
| 38 | Cottonwood STP | Cottonwood | 0.22 | 822 | ID0021849 | Aug 2026 | 22 |
| 39 | Ririe Sewage Lagoons | Ririe | 0.22 | 656 | ID0026174 | Jan 2009 | 0 |
| 40 | Aberdeen WWTP | Aberdeen | 0.2 | 1,756 | ID0020176 | Feb 2021 | 22 |
| 41 | Filer WWTP | Filer | 0.18 | 2,845 | ID0020061 | Oct 2012 | 0 |
| 42 | Parma WWTP | Parma | 0.18 | 2,096 | ID0021776 | Mar 2022 | 89 |
| 43 | Santa Fernwood WWTF | Fernwood | 0.17 | 687 | ID0022845 | May 2025 | 7 |
| 44 | Pierce WWTP | Pierce | 0.17 | 501 | ID0020206 | May 2023 | 1 |
| 45 | Potlatch WWTP | Potlatch | 0.16 | 1,425 | ID0022501 | Nov 2025 | 21 |
| 46 | Elk City WWTP | Elk City | 0.16 | 147 | ID0022012 | Apr 2020 | 2 |
| 47 | Kamiah Regional STP | Kamiah | 0.16 | 2,133 | ID0028002 | May 2028 | 11 |
| 48 | Carey WWTP | Carey | 0.15 | 685 | ID0025747 | Jul 2023 | 15 |
| 49 | Deary WWTP | Deary | 0.14 | 595 | ID0020788 | Jul 2027 | 23 |
| 50 | Mullan WWTP | Mullan | 0.14 | 814 | ID0021296 | Nov 2025 | 33 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Largest plants in Idaho: 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 · MGD · NPDES permit · Filter press · FOG · all terms
Cite this page
Journalists, researchers and educators are welcome to quote these figures. Please credit Klarifi as the source and link to this page.
Klarifi. “The 50 largest wastewater treatment plants in Idaho (2026).” Updated October 26, 2026. https://klarifi.io/facilities/idaho/largestNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.