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Delta-Mendota Subbasin

This website provides information on sustainable groundwater management activities, meetings and resources in the Delta-Mendota Subbasin. The Sustainable Groundwater Management Act, passed in 2014, requires the formation of local Groundwater Sustainability Agencies (GSAs) to oversee the development and implementation of Groundwater Sustainability Plans (GSPs), with the ultimate goal of achieving sustainable management of the State’s groundwater basins. As of June 2017, 23 GSAs have formed in the Delta-Mendota Subbasin. These GSAs have until January 31, 2020 to develop and adopt one or more GSPs for the Delta-Mendota Subbasin.

This website will provide updates on preparation of the GSP(s) for the Delta-Mendota Subbasin, as well as meeting announcements and availability of draft plans, maps and other relevant documents. For more information about the Delta-Mendota Subbasin click here

Quick Facts

Groundwater Basin Number: 5-22.07
County: Stanislaus, Merced, Madera, Fresno
Surface Area: 747,000 acres (1,170 square miles)

The Delta-Mendota Subbasin  is bounded on the west by sediments of the Coast Ranges, and on the north by the Stanislaus/San Joaquin County line. The eastern boundary follows the San Joaquin River to Township 11S, where it jogs eastward and follows the eastern boundary of Columbia Canal Company to the San Joaquin River, then follows the Chowchilla Bypass and the eastern border of Farmer’s Water District. It then trends southerly through Township 14S Range 15E on the eastern side of Fresno Slough, then follows the Tranquillity Irrigation District boundary to its southern extremity. Heading northward, it follows the eastern, northern, and northwestern boundary of San Joaquin Valley – Westside Groundwater Subbasin (corresponding with Westlands Water District boundaries).

The Delta-Mendota Subbasin is designated a high priority basin by the California Department of Water Resource’s (DWR) CASGEM program.

Groundwater Management Plan

The San Luis & Delta-Mendota Water Authority developed a groundwater management plan (also known as a AB 3030 plan) for the northern agencies in the Delta-Mendota Canal Service Area in 1997. In 2011, the plan was updated to respond to new State legislation.

GSAs in the Delta-Mendota Subbasin

There are 23 Groundwater Sustainability Agencies (GSAs) in the Delta-Mendota Subbasin that have submitted formation notices with DWR:

Aliso Water District
Central Delta-Mendota
City of Dos Palos
City of Firebaugh
City of Gustine
City of Los Banos
City of Mendota
City of Newman
City of Patterson
County of Madera—3
Farmers Water District

Fresno County—Management Area ‘A’
Fresno County—Management Area ‘B’
Grassland Water District
Merced County—Delta-Mendota
Northwestern Delta-Mendota
Oro Loma Water District
Patterson Irrigation District
San Joaquin River Exchange Contractors Water Authority
Turner Island Water District-2
West Stanislaus Irrigation District
Widren Water District

For GSA contact information, see the Contacts page. For information about meetings and materials for each agency, see the Meetings page.

Sustainable Groundwater Management Act

In 2014, California lawmakers adopted the Sustainable Groundwater Management Act (SGMA). This far-reaching law seeks to bring the State’s critically important groundwater basins into a sustainable regime of pumping and recharge. SGMA:
  • Establishes a definition of “sustainable groundwater management”
  • Requires that a Groundwater Sustainability Plan (GSP) be adopted for high- and medium-priority groundwater basins in California
  • Establishes a timetable for adoption of GSPs
  • Empowers local agencies to manage basins sustainably
  • Establishes basic requirements for GSPs
  • Provides for a limited state role
SGMA requires by June 30, 2017, the formation of locally-controlled groundwater sustainability agencies (GSAs) in groundwater basins and subbasins (basins) designated as medium or high priority by the California Department of Water Resources (DWR). A GSA is responsible for developing and implementing a GSP. These plans assist groundwater basins in meeting sustainability goals. The primary goal is to maintain sustainable yields without causing undesirable results. There are multiple opportunities for stakeholder and public feedback throughout the SGMA process. See the Get Involved page for more information about upcoming public meetings and previous meeting materials.


The following dates are key milestones for GSAs:

June 30, 2017

All medium and high priority basins are required to establish GSAs or equivalent entities. The State Water Resources Control Board may hold a meeting to designate basin as “probationary” if a GSA or approved alternative is not established.

July 1, 2017

Counties must affirm or disaffirm responsibility as a GSA if no GSA has been established. The State Water Resources Control Board adopts a schedule for “state back-stop”-related costs.

December 15, 2017

The State Water Resources Control Board begins collecting annual reports from persons extracting more than 2 acre-feet per year (AFY) of groundwater from areas not managed by a GSA.

January 31, 2020

High and medium priority basins identified as critically overdrafted must be managed under a GSP. GSAs have 20 years from the date of adopting their GSP to achieve basin sustainability.

January 31, 2022

All other high and medium priority basins must be managed under a GSP. GSAs have 20 years from the date of adopting their GSP to achieve basin sustainability.

Additional Information