What is an irrigation district?

An irrigation district is a local public agency, run by a board its landowners or voters elect, that holds water rights or water contracts and delivers that water through its own canals to the farms inside its boundary. How a district holds its water, through its own senior rights or as a contractor of a federal or state project, decides how much its growers receive in a dry year.

The table shows that difference in a single season. In water year 2026 Reclamation gave Sacramento River Settlement contractors 100% of their contracts on Feb 26, while south-of-Delta agricultural service contractors started at 15% and ended at 28% by Aug 11. Both are farm water from the same Central Valley Project. What separates them is the kind of claim each district holds.

Where irrigation districts came from

California's first irrigation district was Turlock Irrigation District, founded on June 6, 1887 under the Wright Act, a state law passed that year. The Wright Act let a majority of residents in an area form a public entity to deliver water and pay for its dams and canals by selling bonds, which made it possible to build systems no single farmer could afford. Other western states have irrigation districts of their own, and California also has look-alikes organized under other laws, such as California water districts and water storage districts, that do the same job.

What a district does

A district owns or operates the diversion, the main canal and the laterals that carry water to each field. It decides each season how much water is available per acre, sets the delivery rules and charges growers for the water it delivers (Turlock Irrigation District, below, sells it by a rate schedule its board adopts). Growers order water from the district, not from the state or Reclamation, so the district's number is the one that reaches a farm.

Three ways to hold water

• Its own senior rights. A district that holds old appropriative rights to a river takes its water first in a shortage, ahead of anyone whose rights are newer.
• A project contract. A district can contract with Reclamation's Central Valley Project or the State Water Project for a share of the water those projects store and pump. In a dry year the project cuts that share, class by class.
• A blend of both. Some districts held rights before the federal dams were built and signed settlement contracts with Reclamation that recognize them, which is why their allocations are among the last to be cut.

Worked example: three districts in water year 2026

Glenn-Colusa Irrigation District pumps from the Sacramento River near Hamilton City into a 65-mile main canal serving 175,000 acres, about 140,000 of them farmland, mostly rice and nuts. Its water rights date to 1883, older than the district itself, which was organized in 1920. Its Sacramento River Settlement Contract with Reclamation provides 720,000 acre-feet from April to October plus 105,000 acre-feet of project water in July and August. In a critical year, when natural inflow to Shasta Reservoir falls below 3.2 million acre-feet, settlement contractors are cut to 75%, or 618,000 acre-feet for Glenn-Colusa. In 2022 the district's allocation fell to 18%. In 2026 the class received 100%.

Westlands Water District, on the west side of the San Joaquin Valley, was formed on Sep 8, 1952 as a water district, the other legal form. Its growers pumped groundwater until federal water arrived in the 1960s under a 1963 contract for 900,000 acre-feet a year, with 250,000 acre-feet more committed after its 1965 merger with Westplains Water Storage District. As a south-of-Delta agricultural service contractor it took the 2026 path in the table: 15% on Feb 26, 20% on Mar 24, 25% on May 19 and 28% on Aug 11. Applied to the 1,150,000 acre-feet of those original commitments, 28% is about 322,000 acre-feet.

Turlock Irrigation District relies on neither project. It holds Tuolumne River rights jointly with Modesto Irrigation District, which TID describes as the most senior known appropriative rights on the river, the oldest dating to 1871, and stores the water in New Don Pedro Reservoir, which the two districts completed in 1971 with room for 2,030,000 acre-feet.

On Mar 3, 2026 TID's board set the season's supply at 48 inches of water per acre, from Mar 12 to Oct 28, across 145,559 irrigated acres. New Don Pedro held 1,716,331 acre-feet on Feb 23, 2026, 206,247 more than on the same day a year earlier. In 2022, after the reservoir had read 1,189,571 acre-feet on Mar 1, TID set 27 inches. The same district on the same river made 21 more inches per acre available in 2026, going into the season with a fuller reservoir.

Why the district's number matters more than the state's

A statewide allocation or reservoir average says little about a single farm. In 2026 a grower in Glenn-Colusa received the full settlement contract, a grower in Westlands received 28% of a service contract, and a grower in Turlock received 48 inches per acre. How CVP allocations work explains the contractor classes, and CVP and SWP allocations and New Don Pedro Reservoir carry the numbers as they are announced and measured.