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Waterbody profile

Official Water Board record · 2026 cycle

Westlake Lake

Waterbody ID (WBID)
CAL4042500019990201153000
County / counties
Los Angeles, Ventura
Regional Water Board
Regional Board 4 - Los Angeles Region
Waterbody type
Lake & Reservoir
Condition category
Category 5 — 303(d) listed, TMDL required
Integrated Report cycle
2026

303(d) listings (5)

Each row is one official listing decision from Appendix A of the Final 2026 California Integrated Report. Source terminology is preserved as published.

Pollutant / stressorDecision IDFinal listing decisionDecision statusTMDL requirement statusTMDL projectTMDL priority
AlgaeNutrients77046List on 303(d) list (being addressed by USEPA approved TMDL)Original5B Addressed by USEPA-approved TMDLMalibu Creek Nutrients (50)
AmmoniaNutrients77083List on 303(d) list (being addressed by USEPA approved TMDL)Original5B Addressed by USEPA-approved TMDLMalibu Creek Nutrients (50)
EutrophicNutrients77047List on 303(d) list (being addressed by USEPA approved TMDL)Original5B Addressed by USEPA-approved TMDLMalibu Creek Nutrients (50)
LeadMetals72393List on 303(d) list (TMDL required list)Original5A TMDL still requiredLow
Organic Enrichment/Low Dissolved OxygenNutrients76041List on 303(d) list (being addressed by USEPA approved TMDL)Original5B Addressed by USEPA-approved TMDLMalibu Creek Nutrients (50)

Source & provenance

Agency
California State Water Resources Control Board
Report
Final 2026 California Integrated Report
Dataset
Appendix A — 2026 303(d) List of Impaired Waters
Imported
Aug 21, 2026, 12:44 AM UTC
Waterbody ID
CAL4042500019990201153000
CALWNUM
4404.240000, 4404.250000
WBD code
180701040101
Geometry
Official Water Board GIS (CA_WATERBOARDS_GIS_FINAL_2026)

Location

Official 2026 Water Board geometry. Demonstration facility markers are shown for context only.

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Watershed
Assessed size
132.41 Acres

Derived facility associations

Industrial stormwater facilities geographically associated with this waterbody. These are derived spatial associations, not Water Board findings.

Derived
Crane Technology Company Incorporated

Westlake Village · No Exposure Certification · 0.96 km away

derived_nearby_in_watershed

Derived by California Stormwater Intelligence

Elanen Naturals LLC

Westlake Village · No Exposure Certification

derived_watershed_association

Derived by California Stormwater Intelligence

First Sensor Inc

Westlake Village · No Exposure Certification

derived_watershed_association

Derived by California Stormwater Intelligence

Moyer & Associates

Thousand Oaks · No Exposure Certification · 0.97 km away

derived_nearby_in_watershed

Derived by California Stormwater Intelligence

Mrs Williams Country Kitchen

Westlake Village · No Exposure Certification · 0.94 km away

derived_nearby_in_watershed

Derived by California Stormwater Intelligence

PeproTech Inc a part of ThermoFisher

Thousand Oaks · No Exposure Certification

derived_watershed_association

Derived by California Stormwater Intelligence

Rantec Microwave Systems Inc

Westlake Village · Notice of Intent

derived_watershed_association

Derived by California Stormwater Intelligence

The Printing Press

Westlake Village · No Exposure Certification

derived_watershed_association

Derived by California Stormwater Intelligence

The Village Winery

Thousand Oaks · No Exposure Certification · 0.84 km away

derived_nearby_in_watershed

Derived by California Stormwater Intelligence

Thousand Oaks Printing

Westlake Village · No Exposure Certification

derived_watershed_association

Derived by California Stormwater Intelligence

Facility records are official Industrial General Permit registrations, but the association between a facility and this waterbody is derived geographically (proximity or shared HUC12 subwatershed) and is not a Water Board receiving-water determination. Where a permit carries a Water Board-stated TMDL requirement naming this water, it is listed separately above.