What is the largest wastewater treatment plant in California?

Hyperion Treatment Plant in Playa Del Rey, treating an average of 214 MGD under NPDES permit CA0109991. Joint Water Pollution Control Plant in Carson is second at 162.85 MGD.

How much wastewater do California’s largest plants treat?

The 50 largest plants treat 1,051 MGD combined, 96% of the flow reported by all 193 publicly owned plants in California.

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.

Try for free Log in

The 50 largest wastewater treatment plants in California

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

Ranked by average flow · 1,051 MGD combined · 96% of the state's reported flow

Hyperion Treatment Plant in Playa Del Rey is the largest publicly owned wastewater treatment plant in California by reported average flow, treating about 214 million gallons per day. The 50 plants below treat 1,051 MGD between them, 96% of the flow reported by all 193 plants in the state, and serve about 15,579,615 people. Every plant links to its profile with permit, technology and compliance data.

All plants in California →The 100 largest US plants →California NPDES permits →

The 50 largest publicly owned wastewater treatment plants in California by average flow (MGD), with population served, NPDES permit, expiry, treatment technology and three-year violation count.
#	Facility	City	Avg flow (MGD)	Population	NPDES permit	Expires	Technology	Violations (3y)
1	Hyperion Treatment Plant	Playa Del Rey	214	2,800,773	CA0109991	Apr 2028	Clarifiers	42
2	Joint Water Pollution Control Plant	Carson	162.85	3,353,576	CA0053813	Jun 2028	—	19
3	Point Loma Wastewater Treatment Plant	San Diego	137	2,222,389	CA0107409	Sep 2022	Biogas silos	1689
4	Orange County Sanitation District Plant 1	Fountain Valley	77.37	—	CA0110604	Jul 2026	Clarifiers	0
5	Ccsf- Southeast Water Pollution Control Plant	San Francisco	45.87	585,360	CA0037664	Sep 2018	Clarifiers, Biogas silos	13
6	Stockton Rwcf	Stockton	29.2	335,503	CA0079138	Jul 2030	Clarifiers, Uncovered lagoons, Biogas silos	57
7	South Bay International WWTP	San Diego	29	146,085	CA0108928	Jun 2026	Clarifiers, Biogas silos	3159
8	San Jose Creek Water Reclamation Plant	Whittier	28.38	936,523	CA0053911	Nov 2026	—	26
9	Riverside City, Water Quality Control	Riverside	27.72	366,930	CA0105350	Oct 2018	Clarifiers, Aerated lagoons, Uncovered lagoons, Biogas silos, Biogas balloons	2
10	Encina Water Pollution Control Facility	Carlsbad	23.78	94,500	CAL107395	Dec 2030	Clarifiers, Biogas silos	11
11	Colton/san Bernardino Stp, Rix	Colton	21.06	403,461	CA8000304	Jul 2018	Aerated lagoons	0
12	La City , Pub Works Dept	Van Nuys	19	919,987	CA0056227	Jan 2028	—	45
13	Oxnard Wastewater Treatment Plant (owtp)	Oxnard	16.6	212,912	CAL054097	Dec 2030	Clarifiers, Biogas silos	137
14	Valencia Wwrp	Valencia	14.1	168,637	CA0054216	Jun 2027	Biogas silos	5
15	Aliso Creek Ocean Outfall	Dana Point	11.47	45,723	CA0107417	Apr 2027	Biogas silos	32
16	Oceanside Ocean Outfall	Oceanside	10.7	38,102	CA0107433	Mar 2025	Clarifiers, Biogas silos	5
17	Whittier Narrows Water Reclamation Plant	South El Monte	10.24	297,390	CA0053716	Jul 2026	—	14
18	Terminal Island Treatment Plant	San Pedro	9.8	123,833	CA0053856	Jul 2026	—	17
19	Victor Valley Wastewater Reclamation Authority	Victorville	9.48	230,482	CA0102822	May 2025	Clarifiers, Aerated lagoons, Uncovered lagoons, Biogas silos	7
20	City Of Tracy Waste Water Treatment Plant	Tracy	8.9	79,920	CAL079154	Dec 2030	Clarifiers, Biogas silos	11
21	Western Riverside Co Reg WWTP	Corona	8.54	113,419	CA8000316	Jul 2020	Clarifiers, Carrousels / oxidation ditches, Biogas silos	47
22	Forest Shade Sewage Lift Station	Crestline	8.3	90,953	CA0077691	Jul 2029	—	14
23	Hill Canyon WWTP	Camarillo	8.09	117,000	CA0056294	Jul 2031	Clarifiers, Uncovered lagoons, Biogas silos	3
24	Escondido City Of	Escondido	7.8	180,000	CA0107981	May 2023	Clarifiers	2
25	Corona WWTP 1	Corona	7.64	104,926	CA8000383	Jun 2025	Clarifiers, Aerated lagoons, Carrousels / oxidation ditches, Biogas silos	9
26	Michelson Treatment Plant	Irvine	6.99	120,986	CA8000326	Jun 2020	Uncovered lagoons	16
27	Simi Vly Cnty Sanitation	Simi Valley	6.5	114,190	CA0055221	Jul 2031	Clarifiers, Covered lagoons, Uncovered lagoons, Biogas silos	37
28	Chino	Chino	6.4	125,940	CA8000409	Jul 2027	Clarifiers, Biogas silos	519
29	La City, La-Glendale Water Reclamation	Los Angeles	5.9	213,774	CA0053953	Jan 2028	—	7
30	Clear Creek WWTP	Anderson	5.67	65,424	CA0079731	Jul 2027	Clarifiers, Uncovered lagoons, Biogas silos	16
31	Watsonville WWTF	Watsonville	5.21	58,713	CA0048216	Jul 2019	Clarifiers, Biogas silos, Biogas balloons	8
32	Manteca Wwqcf	Manteca	5.18	67,537	CA0081558	Mar 2026	Clarifiers, Uncovered lagoons, Biogas silos	7
33	Yuba City Wastewater Treatment Facility	Yuba City	5.05	47,700	CA0079260	Mar 2024	Clarifiers, Uncovered lagoons, Biogas silos	21
34	Water Reclamation Plant No. 4	Thermal	4.93	—	CA0104973	Apr 2028	Clarifiers, Aerated lagoons, Uncovered lagoons	11
35	Long Beach Water Reclamation Plant	Long Beach	4.44	189,973	CA0054119	Mar 2027	—	5
36	Saugus Wwrp	Saugus	4.3	49,393	CA0054313	Jun 2027	Biogas silos	9
37	San Luis Obispo WWTP	San Luis Obispo	4.23	40,960	CAL049224	Dec 2030	Clarifiers, Uncovered lagoons, Biogas silos	23
38	Henry N. Wochholz Wastewater Treatment Facility	Yucaipa	3.87	58,500	CA0105619	Oct 2020	—	9
39	El Centro WWTP	El Centro	3.7	39,493	CA0104426	Mar 2024	Clarifiers, Aerated lagoons, Uncovered lagoons, Biogas silos	17
40	Camarillo Sanitary Dist Water Reclamation Plant	Camarillo	3.57	62,737	CA0053597	Dec 2024	Clarifiers, Uncovered lagoons, Biogas silos	88
41	Beaumont WWTF	Beaumont	3.54	35,798	CA0105376	Oct 2027	—	14
42	Sewerage Commission - Oroville Region	Oroville	3.4	48,631	CA0079235	Sep 2026	Clarifiers, Aerated lagoons, Uncovered lagoons, Biogas silos	0
43	Davis Water Pollution Control Plant	Davis	3.2	62,764	CA0079049	Jul 2030	Clarifiers, Uncovered lagoons, Biogas silos	41
44	Eureka Wastewater Treatment Plant	Eureka	3.08	41,400	CA0024449	Oct 2028	Aerated lagoons, Uncovered lagoons, Biogas silos	24
45	City Of Morro Bay Water Reclamation Facility	Morro Bay	2.74	—	CA3000002	Aug 2027	—	40
46	Ironhouse Sd WWTP	Oakley	2.71	39,600	CA0085260	Jul 2029	—	9
47	Woodland WPCF	Woodland	2.61	53,100	CA0077950	Mar 2030	Clarifiers, Uncovered lagoons, Carrousels / oxidation ditches	2
48	Calexico Waste Water Plant	Calexico	2.5	36,316	CA7000009	May 2024	Uncovered lagoons	9
49	Linda County WWTP	Marysville	2.41	16,927	CA0079651	Jan 2028	Clarifiers, Uncovered lagoons, Biogas silos	21
50	Redding Stillwater Wastewater Treatment Plant	Anderson	2.32	21,375	CA0082589	May 2028	Clarifiers, Uncovered lagoons	6

Largest plants in California: 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.

Try Klarifi for free

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

Try for free