How many wastewater treatment plants are there in Washington?

Klarifi tracks 150 publicly owned wastewater treatment plants in Washington with a combined average flow of 344 million gallons per day, serving about 3,852,032 residents. 31 of them treat more than 1 MGD and 6 more than 10 MGD.

What is the largest wastewater treatment plant in Washington?

Metro West Point in Seattle is the largest plant in Washington by average flow, treating about 106.93 MGD.

What treatment technologies are common in Washington?

47 of Washington's plants use lagoon systems and 23 have biogas or anaerobic digestion infrastructure, based on Klarifi's aerial imagery review.

How many NPDES permits in Washington are up for renewal?

18 permits held by Washington plants expire in 2026 and 2 in 2027. Renewals typically bring new limits and trigger upgrade projects.

Try for free Log in

Wastewater treatment plants in Washington

Name: Wastewater treatment plants in Washington
Creator: Klarifi
License: https://klarifi.io/terms-of-service

150 facilities · 344 MGD combined flow

Klarifi tracks 150 publicly owned wastewater treatment plants in Washington with a combined average flow of 344 MGD, serving about 3,852,032 residents. 31 plants treat more than 1 MGD and 6 more than 10 MGD; 47 use lagoon systems and 23 have digesters or biogas infrastructure. The largest is Metro West Point in Seattle at 106.93 MGD. 18 NPDES permits expire this year and 2 next year.

Every plant below links to a profile with average and design flow, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city. Treatment technology and verified contacts are shown with a free Klarifi account.

150 plant locations in Washington; dot size follows average flow. Boundaries: U.S. Census Bureau.

NPDES permits and renewals in Washington

Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.

All NPDES permits in Washington →18 permits expiring in 2026 →Find plants near you on the map →

Largest wastewater treatment plants in Washington

The 10 largest publicly owned wastewater treatment plants in Washington by average flow, with NPDES permit, expiry and three-year violation count. Source: EPA ICIS-NPDES via Klarifi.
Facility	City	Avg flow (MGD)	Design (MGD)	NPDES permit	Expires	Violations (3y)
Metro West Point	Seattle	106.93	—	WAL029181	Dec 2030	275
King County South WWTP	Renton	74.4	—	WAR002511	Dec 2029	3
Chambers Creek WWTP	University Place	22.49	—	WAR000727	Dec 2029	0
Three Rivers Regional WWTP	Longview	17.43	52	WA0037788	Feb 2026	0
Post Point Plant	Bellingham	15.62	—	WAR005561	Dec 2029	1
Lott Wastewater Treatment Plant	Olympia	12.08	—	WAG994545	Dec 2026	0
Yakima Regional Wastewater Facility	Yakima	8.67	—	WA0024023	Mar 2029	2
Richland City Wastewater Lab	Richland	5.91	22.8	WA0020419	Sep 2021	0
Puyallup WWTP	Puyallup	5.2	—	WAR313277	Dec 2030	0
Lakota WWTP	Federal Way	4.96	—	WA0022624	Sep 2023	4

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

The 50 largest plants in Washington →EPA enforcement actions in Washington →Washington capital improvement plans →

Washington plants by treatment technology

Activated sludge and clarifiers (74)Lagoon systems (47)Oxidation ditches (36)Anaerobic digesters and biogas (23)

All 150 plants in Washington

Facility	City	Flow (MGD)
Metro West Point	Seattle	106.93
King County South WWTP	Renton	74.4
Chambers Creek WWTP	University Place	22.49
Three Rivers Regional WWTP	Longview	17.43
Post Point Plant	Bellingham	15.62
Lott Wastewater Treatment Plant	Olympia	12.08
Yakima Regional Wastewater Facility	Yakima	8.67
Richland City Wastewater Lab	Richland	5.91
Puyallup WWTP	Puyallup	5.2
Lakota WWTP	Federal Way	4.96
Lynnwood City Wastewater Treatment Plan	Edmonds	3.96
Miller Creek WWTP And Compost Facility	Seattle	3.6
Ellensburg WWTP	Ellensburg	3.59
Salmon Creek WWTP	Seattle	3.03
Wenatchee Wastewater Treatment Plant	Wenatchee	2.86
Port Angeles WWTP	Port Angeles	2.72
Pullman City Muni SW	Pullman	2.46
Picnic Point Wastewater Treatment Facility	Edmonds	2.45
Ferndale STP	Ferndale	2.26
Port Orchard WWTP	Port Orchard	1.98
Enumclaw STP	Enumclaw	1.85
Monroe STP	Monroe	1.79
Port Of Sunnyside Industrial WWTF	Sunnyside	1.64
Burlington WWTP	Burlington	1.56
Lynden STP	Lynden	1.56
Sunnyside STP	Sunnyside	1.34
Hoquiam STP	Hoquiam	1.19
Birch Bay Water And Sewer District WWTP	Blaine	1.17
Cle Elum WWTP	Cle Elum	1.13
Washougal STP	Washougal	1.09
Willapa Regional WWTF	Raymond	1.01
Sedro Woolley City Of	Sedro-Woolley	0.96
Grandview Wastewater Treatment Plant	Grandview	0.93
Orting STP	Orting	0.91
Othello STP	Othello	0.89
College Place WWTP	Walla Walla	0.87
Port Townsend WWTP	Port Townsend	0.83
Chelan WWTP	Chelan	0.75
Prosser City WWTP	Prosser	0.74
Clarkston WWTP	Clarkston	0.69
Stanwood STP	Stanwood	0.67
Toppenish Wastewater Treatment Plant	Toppenish	0.66
Sequim Water Reclamation Facility	Sequim	0.64
Bainbridge Island WWTP	Bainbridge Island	0.63
Sultan WWTP	Sultan	0.59
Naches STP	Naches	0.54
Winlock Wastewater Treatment Plant	Winlock	0.54
Omak Wastewater Treatment Plant	Omak	0.54
Kalama Wastewater Treatment Plant	Kalama	0.49
Lighthouse Point Water Reclamation Facility	Blaine	0.42
Cashmere STP Facility	Cashmere	0.42
Granite Falls STP	Granite Falls	0.41
Friday Harbor STP	Friday Harbor	0.4
Medical Lake WWTP	Medical Lake	0.38
Ridgefield WWTP	Ridgefield	0.37
Castle Rock STP	Castle Rock	0.37
Chewelah WWTP	Chewelah	0.37
Everson WWTP	Everson	0.33
Colfax Wastewater Treatment Plant	Colfax	0.33
Bingen POTW	Bingen	0.32
Pe Ell STP	Pe Ell	0.31
La Center STP Aspen Ave	La Center	0.31
Stevenson STP	Stevenson	0.31
Leavenworth STP	Leavenworth	0.3
La Conner STP	Mount Vernon	0.28
Montesano Sewage Treatment Plant	Montesano	0.27
Dayton STP	Dayton	0.25
Eatonville STP	Eatonville	0.24
Cathlamet Former Sewage Lagoons	Cathlamet	0.23
Benton City STP	Benton City	0.23
Ilwaco Wastewater Treatment Plant	Ilwaco	0.22
Manchester WWTP	Port Orchard	0.22
Grand Coulee WWTP	Grand Coulee	0.2
Zillah Wastewater Treatment Plant	Zillah	0.2
Tulalip Wastewater Treatment Plant	Marysville	0.2
Big Lake WWTP	Mount Vernon	0.19
Lummi Kwina Road WWTP	Bellingham	0.18
Kittitas POTW	Kittitas	0.18
Oroville Wastewater Treatment Plant	Oroville	0.18
Grand Mound STP	Rochester	0.17
Granger POTW	Granger	0.17
Newport WWTP	Newport	0.17
Kitsap Cnty Kingston WWTP	Kingston	0.16
Pacific Beach STP	Pacific Beach	0.16
Okanogan WWTP	Okanogan	0.16
Brewster STP	Brewster	0.16
Waitsburg STP	Waitsburg	0.16
Davenport WWTP	Davenport	0.16
Mabton Wastewater Treatment Plant	Mabton	0.15
Bridgeport WWTP	Bridgeport	0.15
Olympic Corrections Center	Forks	0.13
Pomeroy Sewage Treatment Plant	Pomeroy	0.12
Tekoa STP	Tekoa	0.12
Rosalia STP	Rosalia	0.11
Toledo STP	Toledo	0.1
Ryderwood STP	Ryderwood	0.1
Entiat POTW	Entiat	0.1
Ione STP	Ione	0.1
Tonasket POTW	Tonasket	0.1
Clallam Bay Correction Center STP	Clallam Bay	0.09
Concrete STP	Concrete	0.09
Oakesdale STP	Oakesdale	0.09
Yakama Legends Casino Hotel	Toppenish	0.09
Colton STP	Colton	0.08
Buena WWTF	Zillah	0.08
Endicott STP	Endicott	0.08
Sekiu STP	Sekiu	0.07
Twisp WWTP	Twisp	0.07
Rockford WWTP	Rockford	0.07
Palouse Wastewater Treatment Plant	Palouse	0.07
North Bonneville STP	North Bonneville	0.07
St John WWTP	Saint John	0.07
Onalaska Wastewater Treatment Plant	Chehalis	0.07
Asotin STP	Clarkston	0.06
Toutle STP	Toutle	0.06
Fairfield WWTP	Fairfield	0.06
Rock Island WWTP	Rock Island	0.06
Reardan Town STP	Reardan	0.06
Wa Doc Cedar Creek Correctional Ctr	Littlerock	0.05
Winthrop Wastewater Treatment Plant	Winthrop	0.05
Peshastin Wastewater Treatment Plant	Peshastin	0.05
Odessa STP	Odessa	0.04
Clallam Bay STP	Clallam Bay	0.04
Harrah WWTP	Harrah	0.03
Carbonado STP	Carbonado	0.03
Lyle POTW	Lyle	0.03
Tamoshan WWTP	Olympia	0.03
Lewis County Water And Sewer District 6 STP	Mossyrock	0.02
Klickitat Pud WWTF	Lyle	0.02
Fisherman Bay STP	Lopez Island	0.02
Crescent Bar Inc	Quincy	0.02
Spangle STP	Spangle	0.02
Lake Wenatchee WWTP	Leavenworth	0.02
Moclips River Estates WWTP	Moclips	0.02
Wishram Wastewater Treatment Plant	Wishram	0.01
Vantage STP	Ellensburg	0.01
Metaline STP	Metaline	0.0094
Stevens Pass STP	Leavenworth	0.008
Eastsound Orcas Village WWTP	Orcas	0.0063
Larrabee State Park	Bellingham	0.0032
Fort Flagler State Park	Nordland	0.0028
Cowlitz Indian Tribe - Lewis County WWTF	Toledo	0.002
Selkirk Schools And WWTP	Metaline Falls	0.00082
Rustlewood STP	Shelton	0.000000032
Pasco WWTP	Pasco	—
Salmon Creek WWTP	Vancouver	—
Wa Dnr Larch Mountain Corr	Yacolt	—
Walla Walla Water Reclamation Facility	Walla Walla	—
Wilbur STP	Wilbur	—
Yelm WWTP	Yelm	—

Wastewater treatment in Washington: 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 · Lift station · Inflow and infiltration · 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. “Wastewater treatment plants in Washington.” Updated October 26, 2026. https://klarifi.io/facilities/washington

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

Try Klarifi for free

Create your own trial account and explore how Klarifi can help you.

Try for free