For the agencies that deliver water to California's farms and cities, the Delta is the single most critical link in the statewide water system.
For anglers and environmentalists, it is a pivotal natural resource of huge biological importance.
For a half-million Contra Costa residents, it is the sole source of drinking water.
It is criss-crossed by major highways, railroad lines, ship channels and aqueducts that supply water to San Francisco, Oakland and other Bay Area cities. Northern California's largest natural gas storage facility is in the Delta.
It has more than 500,000 acres of farms that grow grains, hay, asparagus, tomatoes and other crops.
There are 230 species of birds and 50 species of fish. The Delta is a stopover on the Pacific Flyway and a highway for most of California's migrating salmon.
Tens of thousands of boaters are in the Delta, as are cities such as Antioch and Brentwood.
So much is asked of it.
And it is failing.
Its levees are vulnerable. Its ecosystem is in deep trouble. Its water quality is worsening and its dependability as a water source for 7 million acres of farmland in the San Joaquin Valley and 23 million Southern Californians is weakening.
"There's a lot of agreement that CalFed hasn't managed the Delta effectively and a revitalized CalFed program has to focus on Delta management," said Barry Nelson, a water policy analyst at the Natural Resources Defense Council.
Next month, CalFed officials plan to begin a two-year process to come up with a new vision for the Delta. A panel of scientists will assemble what is known about the Delta, and that will be followed by a public -- and likely contentious -- process to develop a template for what the Delta should be in 100 years.
"I actually think we're on the right track," said Jeff Mount, a UC Davis geologist who says the way the Delta is now being used in unsustainable.
"The dialogue has begun about alternative futures of the Delta. That's a huge change, because up to now, all the talk was based on a future Delta looking like what it looks like now," Mount said. "This really should have been done by CalFed, and CalFed (has been) about completely out of the loop on that."
The planning will be broadly focused, but one issue will loom large. The CalFed plan that was signed five years ago set a 2007 deadline for a re-evaluation to address a major question: Can the Delta reliably convey water from Northern California to points south?
If not, CalFed would consider taking water out of the Sacramento River, north of the Delta, and sending it around the Delta in canals or pipes.
That proposal would be enormously controversial. It harkens back to the late 1970s and early 1980s, when state water officials and Southern Californians wanted to build the Peripheral Canal, a huge canal capable of moving portions of the Sacramento River's flow around the Delta. The original Peripheral Canal would have been capable, at times, of drying up California's largest river.
Consideration of any such canal will certainly be smaller in scale this time around. Some environmentalists say a smaller canal might now make sense.
But even a smaller diversion would raise serious concerns in Contra Costa because the Delta's water quality would deteriorate further and could conceivably force the Contra Costa Water District to desalinate its water.
The district, which serves 500,000 residents, has already spent hundreds of millions of dollars in the last decade to counter the continued degradation of the Delta's water quality.
It built the $450 million Los Vaqueros Reservoir to capture higher-quality water to be used when the Delta is salty. It implemented new water treatment techniques and built a new treatment plant.
The prospect of spending even more -- and sending more water to Southern California -- will set off a lively debate, predicted water district assistant general manager Greg Gartrell.
"This is the third rail of California water. It will light things up," he said.