The Sacramento and San Joaquin Delta, formed where the two rivers meet in California’s Central Valley before flowing into San Francisco Bay, is the largest estuary on the entire West Coast of the Americas. But much of the Delta is a remote, labyrinthine wateriness that, for most people, exists only in the mind, wrapped in an impenetrable mist.

Yet without the Delta, California — at least as people generally think of the place — would not exist. Two-thirds of the water used in the state is drafted from the Delta by two sets of enormous pumps that form the heart of the largest water-supply system in the United States. That system — composed of the federally operated Central Valley Project canals and the State Water Project canals — sustains 4.5 million acres of farmland in the San Joaquin Valley along with 23 million people in homes and businesses in Los Angeles, San Diego and elsewhere.

Delta water pulses through the lives — and the bodies — of most Californians and keeps much of the state’s economy afloat. The food grown with it travels to every corner of the country and beyond.

The Delta has also become a source of vexation, as California struggles to keep once-bountiful Delta fish like salmon — the defining icon of Fisherman’s Wharf and the California coast — from spiraling to extinction, while keeping the pumps running full-throttle. Over the past 18 years, powerful interests, including farmers, city water bosses, environmentalists and government regulators, have endured four arduous efforts to achieve that balance, with little success. Just over a year ago, in October 2009, amid rising tensions over dramatic cutbacks in the pumping and a seemingly irreversible fisheries collapse, Gov. Arnold Schwarzenegger launched a fifth attempt. He pressured the Legislature to pass a sweeping package of bills, forcing a scramble to craft a plan that will shape the fate of the Delta for the next half century.