LOS ANGELES -- The FBI's investigation of a state lawmaker has brought attention to an arm of government that is at once indispensable and nearly invisible -- public agencies that pipe water to millions of people and vast swaths of farmland yet operate with scant oversight or public scrutiny.

In a state where water, the economy and politics are intertwined, California has hundreds of local agencies that oversee the pumps and pipes that bring water to fields, homes, schools and industry. Yet the agencies' board elections are often ignored by voters, and little attention is paid to the six-figure salaries, generous pensions and hundreds of millions of dollars in contracts they hand out.

Dozens of water agencies throughout California even ignore the annual requests by the state controller's office to provide salary and staffing information so it can be available publicly. Such agencies typically break into the headlines only when something goes wrong.

"They are completely under the radar," said Robert Stern, former president of the Center for Governmental Studies in Los Angeles. "Who are these people? Yet, they have lots of power."

FBI agents searched state Sen. Ron Calderon's two Sacramento offices last month. They also have sought to question his brother, former Assemblyman Tom Calderon, while at least one other state senator has been subpoenaed to appear before a federal grand jury in Los Angeles.

Three people who have spoken multiple times with the FBI have told The Associated Press that agents initially were interested in virtually anything involving the brothers but more recently narrowed their questions to issues surrounding the Central Basin Municipal Water District, which serves more than 2 million people in working-class and industrial neighborhoods on the fringe of Los Angeles.

Attorneys for the Calderon brothers have said their clients did nothing wrong. Ron Calderon said he couldn't comment on the ongoing investigation, and he intends to keep his Senate seat. Tom Calderon told The Sacramento Bee that "enemies of Central Basin" are making false allegations.

Neither the FBI nor the U.S. Attorney's Office in Los Angeles has commented, citing the secrecy of grand jury proceedings.

The district had been paying Tom Calderon $11,000 per month as a consultant. And agents wanted to know about Ron Calderon's involvement in legislation favoring the small agency, which employs about 20 people.

The three people spoke on condition of anonymity because of concerns the FBI would be upset by public comments about an ongoing investigation.

District officials confirm the agency has received a subpoena but would not comment on details. The agency will "fully cooperate with the investigation," board member Leticia Vasquez said.

The potential link to the Central Basin district in the federal investigation is only the most recent example of a local water district becoming the subject of public scrutiny because of potential misdeeds.

Previous scandals involving water agencies have uncovered fraud, bribes and lavish expenses and travel.

The number of local water agencies in California is staggering and each has its own bureaucracy. The Association of California Water Agencies represents nearly 440 public agencies accounting for about 90 percent of the state's water use.