California

Hmm.

Those people may be necessary, but is this something that can be replicated by providing similar people at a state government level?

The Bureau of Reclamation operates major California dams including the Shasta Dam, as well as the C.W. “Bill” Jones Pumping Plant, which draws water from the Delta and sends it flowing south in the Delta-Mendota Canal.

That's infrastructure internal to California. I don't think that it provides water to other states. I could imagine operating a dam in California at the state government level.

California more or less has borders mapping to watershed boundaries.

I think that the same might not be true of, say states in the Great Plains, where the geography differs; water is also a limiting factor there, but any decision there also impacts users downstream in other states.

https://en.wikipedia.org/wiki/California_State_Water_Project

The SWP shares many facilities with the federal Central Valley Project (CVP), which primarily serves agricultural users.

Say the federal infrastructure, CVP, were folded into the state SWP. That'd decrease federal funds going to California, and I'd imagine that California might want to go renegotiate who gets what on a state-by-state basis.

But generally-speaking, in terms of organization, I'd expect that things be done at a lower level of government unless there's a good reason to shift them upwards. Having an impact that crosses state boundaries would be a good reason for something to be federal...but it doesn't sound to me like that's clearly the case for agricultural water provision in the Central Valley. I don't see why residential water would be handled by state and agricultural water by federal. According to Wikipedia, it sounds like the original intent was to do this at a state level, and the fact that it became federal was largely an artifact of history:

https://en.wikipedia.org/wiki/Shasta_Dam

Initially, the state of California intended to finance the project entirely on its own through the sale of revenue bonds. However, the 1930s were a time of economic crisis with the onset of the Great Depression and a severe drought that devastated the agricultural sector, pushing the unemployment rate in California up to 20 percent. The project was approved in the state legislature by a slim margin, mostly riding on Central and Northern California voters, who needed both the jobs and the water. Southern California generally opposed the project because they needed money to build an aqueduct to the Colorado River, from which the state had previously secured rights.[16] In 1933, the state authorized the sale of bonds to fund the Central Valley Project, whose main component was to be Shasta Dam.[6][10] Unable to raise the necessary money, California turned to the federal government for help.[17]