Lagoon systems: wastewater treatment plants in Idaho
64 plants · 68% of the state · 77 MGD reported by 23 plants
Klarifi identifies 64 publicly owned wastewater treatment plants with lagoon systems in Idaho, 68% of the 94 plants in the state (77 MGD reported by 23 plants). The largest is West Boise WWTP in Garden City at 62 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 Idaho
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | West Boise WWTP | Garden City | 62 | ID0023981 | Jun 2027 | 9 |
| 2 | Pocatello City WWTP | Pocatello | 6.79 | ID0021784 | Aug 2017 | 8 |
| 3 | Emmett WWTP | Emmett | 1.76 | ID0020311 | Jan 2007 | 2 |
| 4 | Star WWTP | Star | 1.58 | ID0023591 | Apr 2020 | 0 |
| 5 | Page WWTP | Smelterville | 1.36 | ID0021300 | Sep 2018 | 1 |
| 6 | Salmon Sewage Lagoon | Salmon | 1.02 | ID0020001 | May 2026 | 0 |
| 7 | Homedale WWTP | Homedale | 0.5 | ID0020427 | Sep 2018 | 18 |
| 8 | Driggs WWTP | Driggs | 0.39 | ID0020141 | Dec 2015 | 163 |
| 9 | Buhl WWTP | Buhl | 0.29 | ID0020664 | Oct 2012 | 2 |
| 10 | St Anthony Sewage Lagoon | Saint Anthony | 0.26 | ID0020401 | Nov 2014 | 7 |
| 11 | Shoshone WWTP | Shoshone | 0.13 | ID0023728 | Apr 2024 | 22 |
| 12 | Council WWTP | Council | 0.12 | ID0020087 | Aug 2025 | 3 |
| 13 | Kooskia WWTP | Kooskia | 0.11 | ID0021814 | Dec 2024 | 21 |
| 14 | Parma WWTP | Parma | 0.11 | ID0021776 | Mar 2022 | 82 |
| 15 | Wilder WWTP | Wilder | 0.08 | ID0020265 | May 2010 | 8 |
| 16 | Horseshoe Bend WWTP | Horseshoe Bend | 0.07 | ID0021024 | Jul 2023 | 3 |
| 17 | Hansen STP | Hansen | 0.07 | ID0022446 | Oct 2012 | 7 |
| 18 | Mackay WWTP | Mackay | 0.07 | ID0023027 | May 2023 | 5 |
| 19 | Smelterville WWTP | Smelterville | 0.06 | ID0020117 | Sep 2018 | 21 |
| 20 | Firth WWTP | Firth | 0.05 | ID0024988 | Mar 2018 | 0 |
| 21 | Troy WWTP | Troy | 0.04 | ID0023604 | Jul 2027 | 26 |
| 22 | Culdesac WWTP | Culdesac | 0.03 | ID0024490 | Sep 2028 | 58 |
| 23 | Kendrick WWTP | Kendrick | 0.01 | ID0024554 | Aug 2023 | 32 |
| 24 | Bonners Ferry WWTP | Bonners Ferry | — | ID0020222 | Oct 2016 | 1 |
| 25 | Bovill Wastewater Treatment Facility | Deary | — | ID0022861 | Nov 2028 | 14 |
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 Idaho
Lagoon systems in other states
Lagoon systems 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 September 11, 2026.