What is the largest wastewater treatment plant in Oregon?

Willow Lake WWTP in Salem, treating an average of 42.45 MGD under NPDES permit ORL026409. Durham Waste Handling in Tigard is second at 24.25 MGD.

How much wastewater do Oregon’s largest plants treat?

The 50 largest plants treat 167 MGD combined, 94% of the flow reported by all 127 publicly owned plants in Oregon.

How is plant size measured?

By reported average daily flow in million gallons per day (MGD) from EPA discharge monitoring reports, the standard measure of a plant’s size. Design capacity, the flow a plant is permitted to treat, is usually higher and is shown on each profile.

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The 50 largest wastewater treatment plants in Oregon

Name: Largest wastewater treatment plants in Oregon
Creator: Klarifi
License: https://klarifi.io/terms-of-service

Ranked by average flow · 167 MGD combined · 94% of the state's reported flow

Willow Lake WWTP in Salem is the largest publicly owned wastewater treatment plant in Oregon by reported average flow, treating about 42.45 million gallons per day. The 50 plants below treat 167 MGD between them, 94% of the flow reported by all 127 plants in the state, and serve about 1,181,938 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.

All plants in Oregon →The 50 largest US plants →Oregon NPDES permits →

The 50 largest publicly owned wastewater treatment plants in Oregon by average flow (MGD), with population served, NPDES permit, expiry and three-year violation count.
#	Facility	City	Avg flow (MGD)	Population	NPDES permit	Expires	Violations (3y)
1	Willow Lake WWTP	Salem	42.45	284,938	ORL026409	Dec 2030	2
2	Durham Waste Handling	Tigard	24.25	53,093	ORL028118	Dec 2030	6
3	Medford Rwrf	Central Point	16.52	159,933	OR0026263	Jul 2026	1
4	Gresham WWTP	Portland	11.55	126,805	OR0026131	Aug 2026	0
5	Albany-Millersburg WRF	Albany	8.27	52,976	OR0028801	Jan 2031	2
6	Tryon Creek WWTP	Lake Oswego	5.22	86,722	OR0026891	Apr 2029	2
7	Mcminnville WWTP	Mcminnville	4.99	34,615	OR0034002	Dec 2008	2
8	Grants Pass STP	Grants Pass	4.92	49,734	OR0028843	Sep 2014	16
9	Astoria STP	Astoria	4.38	10,404	OR0027561	Oct 2016	14
10	Lebanon STP	Lebanon	3.82	17,335	OR0020818	Oct 2030	39
11	Oak Lodge Water Reclamation Facility	Milwaukie	3.05	35,370	OR0026140	Mar 2027	3
12	Dallas WWTP	Rickreall	2.77	16,555	OR0020737	Oct 2030	16
13	Lincoln City STP	Lincoln City	2.51	14,102	OR0020478	Mar 2031	2
14	Sweet Home STP	Sweet Home	1.88	9,718	OR0020346	Mar 2010	27
15	Ontario STP	Ontario	1.87	11,515	OR0020621	Jan 2031	2
16	Ashland WWTP	Ashland	1.67	21,788	OR0026255	Jan 2027	13
17	Seaside WWTP	Seaside	1.65	6,875	OR0020401	Jul 2029	27
18	Monmouth STP	Monmouth	1.56	9,940	OR0020613	Dec 2030	3
19	Hermiston WWTP	Hermiston	1.48	18,775	OR0020761	Jan 2028	0
20	Hood River STP	Hood River	1.3	8,717	OR0020788	May 2031	45
21	Lakeview STP	Lakeview	1.24	—	OR0041386	Jul 2031	143
22	Junction City STP	Junction City	1.19	8,977	OR0026565	Oct 2028	167
23	Prineville STP	Prineville	1.17	10,355	OR0023612	Dec 2016	51
24	Independence STP	Independence	1.02	11,355	OR0020443	Aug 2027	10
25	Scappoose STP	Scappoose	1.02	7,610	OR0022420	Oct 2014	1
26	Canby WWTP	Canby	0.98	16,800	OR0020214	Nov 2027	0
27	Sutherlin WWTP	Oakland	0.94	8,787	OR0020842	Nov 2029	1
28	Estacada STP	Estacada	0.93	4,035	OR0020575	Sep 2015	44
29	Nehalem Bay STP	Nehalem	0.87	3,218	OR0023370	Jun 2028	0
30	Coquille City Shop And Waste Water Plant	Coquille	0.81	3,920	OR0026247	Jul 2029	56
31	Harrisburg Lagoon Treatment Plant	Harrisburg	0.8	3,695	OR0033260	Aug 2027	0
32	Veneta STP	Veneta	0.78	4,845	OR0020532	Jun 2017	8
33	Philomath WWTP	Corvallis	0.75	5,431	OR0032441	Jun 2017	11
34	Toledo STP	Toledo	0.7	3,709	OR0020869	Nov 2010	31
35	Florence STP	Florence	0.69	7,588	OR0020745	Apr 2019	0
36	Myrtle Point STP	Myrtle Point	0.67	2,535	OR0020435	May 2029	58
37	Umatilla STP	Umatilla	0.67	6,574	OR0022306	Dec 2027	0
38	Aumsville STP	Aumsville	0.65	4,000	OR0022721	Aug 2026	5
39	Myrtle Creek WWTP	Myrtle Creek	0.6	8,400	OR0028665	Sep 2008	0
40	Cannon Beach WWTF	Cannon Beach	0.59	1,718	OR0020222	Jul 2030	3
41	Depoe Bay STP	Depoe Bay	0.55	4,943	OR0026107	Jan 2029	0
42	Willamina STP	Willamina	0.48	2,034	OR0022713	Nov 2015	1
43	Carlton STP	Carlton	0.45	2,319	OR0020541	Jun 2015	66
44	Oakridge STP	Westfir	0.45	3,479	OR0022314	Apr 2012	26
45	Lafayette STP	Lafayette	0.42	4,338	OR0022551	Mar 2031	6
46	Gervais STP	Gervais	0.41	2,570	OR0027391	Nov 2015	0
47	Vernonia STP	Vernonia	0.39	2,561	OR0022560	Nov 2029	8
48	Rainier STP	Rainier	0.39	1,940	OR0020389	Jul 2017	30
49	Bay City STP	Bay City	0.39	1,462	OR0022578	Sep 2029	0
50	Jefferson Wastewater Treatment Plant	Jefferson	0.37	2,830	OR0020451	Sep 2016	4

Treatment technology for each plant is shown with a free Klarifi account. Create one →

Largest plants in Oregon: 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 · Activated sludge · Oxidation ditch · 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 Oregon (2026).” Updated October 26, 2026. https://klarifi.io/facilities/oregon/largest

Need a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.

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