When it comes to water, California tends to view itself as a self-contained system-and this perception is not without merit. Except for water diverted from the Colorado River along the state's southeastern border, water supplies in the state are derived solely from precipitation that falls on California's many watersheds.

But as in the other 49 states, California does not manage this water alone. As climate expert Daniel Swain explained in an interview with us last week, the federal government is a critical partner in water and weather forecasting, and declining federal involvement in these areas will have consequences for the state.

The federal government is also a key partner in California's overall water management, and here too, the current administration looks likely to shrink the role of the federal government. As these policies continue to unfold, we take stock of just how involved the federal government is in the day-to-day management of California's water.

Headwater forests

Headwater forests in California are the source of two-thirds of the state's water. Strong land management in these areas is crucial to maintaining water quality and protecting water infrastructure. Multiple federal agencies own and manage around half the land in the headwater regions, with the US Forest Service managing the largest tracts of land. In the Sierra Nevada and southern Cascade Mountains, which are home to the most critical water sources, that ownership rate rises to 70%. Although the state contributes a significant amount to managing these forests-thanks to recent passage of bond initiatives-most expenditures for fuel reduction to reduce wildfire severity are federal. And the federal government is a key partner during wildfire emergencies.

Water supply

The federal government is equally important to water supply management. At the top of list is the federally owned and operated Central Valley Project, a sprawling water supply project that supports farms and cities in the Central Valley along with some San Francisco Bay Area communities. It includes Shasta Reservoir, the largest reservoir in California, and hundreds of miles of aqueducts. The Central Valley Project also works closely with the State Water Project to supply water to nearly 30 million Californians. In addition, the federal government serves as the de facto watermaster for the Colorado River, where tensions are high between the seven states that rely on the river as supplies have dwindled since 2000 due to persistent drought.

The federal government invests heavily in water management, particularly on farms. Both the US Department of Agriculture (USDA) and the Bureau of Reclamation support efforts to improve water supply reliability and on-farm conservation. USDA's Natural Resource Conservation Service (NRCS) coordinates with the Bureau on WaterSMART program investments that prioritize water conservation and drought resilience. (Federal investment in WaterSMART projects totaled over $4.3 billion in 2024 alone for both municipal and agriculture projects.) And NRCS houses the Environmental Quality Incentives Program, or EQIP, which pays farmers for implementing improved water management systems. Between 2017 and 2022, EQIP payments in California totaled nearly half a billion dollars.

Flood management

The federal government plays a crucial yet underappreciated role in river and coastal flood management. Here the federal government is involved in all phases of reducing flood risk. The US Army Corps of Engineers usually takes on the role of planning, designing, and estimating the costs and benefits of flood projects. Congress is the largest funder of large flood control infrastructure projects, typically providing 50-75% of the funding, and the Army Corps of Engineers often leads construction efforts. The Corps also prescribes how to manage the state's many reservoirs during floods.

Communities throughout the state rely on Federal Emergency Management Agency (FEMA) flood hazard maps to develop land use zoning and establish construction standards. The National Flood Insurance Program provides most flood insurance policies for businesses and homes on the floodplains. And during flood emergencies, the Army Corps of Engineers and FEMA support state and local governments in flood fighting and recovery.

Protecting native biodiversity and endangered species

Finally, two agencies-the US Fish and Wildlife Service and the National Marine Fisheries Service-play a large role in protecting native biodiversity and setting regulatory standards to protect endangered species. And the Environmental Protection Agency oversees the state's administration of the Clean Water Act, which protects water quality for all uses. These three agencies, along with the Army Corps of Engineers, the Bureau of Reclamation, the Forest Service, and others also invest in habitat restoration projects throughout the state.

This is just a short list of how the federal government is involved in California water. But it is intended to highlight a policy question: how should the state respond if the federal government reduces its involvement and investments in California water management? With many of these federal agencies already experiencing reductions in their labor force and more reductions planned, a diminished federal partner may be in California's future.