Delta-Mendota Subbasin

NEW! On April 7, 2026, the State Water Resources Control Board (State Water Board or Board) determined that a probationary designation for the Delta-Mendota Subbasin was not necessary and that the Board would return the subbasin to the Department of Water Resources’ (DWR) jurisdiction.

On March 2, 2023, DWR determined that the Delta-Mendota Subbasin's July 2022 Groundwater Sustainability Plans (GSPs) were inadequate. DWR's determination temporarily shifted primary regulatory oversight of the subbasin to the State Water Board. The groundwater sustainability agencies (GSAs) for the Delta-Mendota Subbasin adopted a single revised GSP in July 2024.

State Water Board staff reviewed the July 2024 GSP and determined the Delta-Mendota Subbasin GSAs addressed the deficiencies identified in DWR’s Inadequate Determination and additional issues identified by Board staff.