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If politicians are correct a perfect storm is bearing down on the Sacramento-San Joaquin Delta, a labyrinth of wetlands, channels and islands that is a vital hub in California's vast water management system that supplies fresh water to a US$32 billion ($40 billion) agribusiness and 25 million people.
Earlier this month, state lawmakers said that the delta levee system - 1770km of earth embankments, some a century old - that helps channel fresh water from the Sacramento and San Joaquin rivers into two huge aqueducts that flow through the San Joaquin Valley into Southern California, was on the verge of collapse.
"There is substantial evidence that the delta is completely broken," Department of Water Resources director Lester Snow said. "We need to invest significantly."
In February, a Public Policy Institute of California report warned, "Over the next 50 years there is a two-thirds chance of a catastrophic levee failure in the delta."
Ellen Hanak, a senior fellow at the institute, says a levee failure might have a domino effect if salt water flooded inland from San Francisco Bay.
The interruption to fresh water supplies could cost as much as US$40 billion and have a huge negative impact on the world's eighth largest economy.
The 300ha delta is an explosive issue in California. The ecosystem has been vanishing since the 1850s when levees were first built, sometimes on peat with poor foundations, to exploit rich soils.
The levee system, which includes 2575km of dykes in the San Joaquin Valley, a vast floodplain, is managed by farmers, state officials and the Army Corp of Engineers.
A levee collapse three years ago, and Hurricane Katrina's devastating impact on New Orleans, has raised concerns for the tens of thousands of people who live behind levees on floodplains.
The earthquakes, subsidence and water seepage that makes levees vulnerable are always a concern and global warming raises the ante.
Water regulators worry about inundation from storm surges fed by rising sea levels, plus flooding as precipitation in the Sierra Nevada range shifts from snow, once a frozen reservoir, to rain.
An expected population rise from 36 to 60 million people by 2050 adds to lawmakers' worries.
As this semi-desert region imports about half its water, guaranteeing supplies is a priority. The situation is made worse by drought. Only 81.5mm of rain has fallen on Los Angeles in the past year (385.6mm is the average) making it the driest year since records began in 1877. Scientists worry that climate change will deepen this crisis.
The state faces huge crop losses from drought and Governor Arnold Schwarzenegger says California's precarious water infrastructure demands "a comprehensive plan for conveyance, storage and conservation", possibly a canal to carry water from the Sacramento River around the delta. This idea is resisted by delta farmers, who helped sink a 1982 canal plan.
Some worry that talk of a more eco-friendly canal disguises a "water grab" by the south.
"I'm compelled to say that the alarmist comments - that the system is on the brink of collapse - are politically motivated," says Jane Wolff, author of Delta Primer: A Field Guide to the California Delta. "It's true that the levees are old, but not fair to say they are crumbling."
Wolff, who advocates fortifying levees near the sea where seismic threats are acute, worries that a canal may negate the need for delta levee maintenance.
Failure could produce "a brackish inland sea" and pollute groundwater - the delta farmers' nightmare.
She is troubled that the state hasn't said how much water it would divert from the delta into a canal.
Spiralling water demands in the south, reduced flows from the Colorado River, and the effects of earlier water-grabs strengthen the argument for a canal.
Voters approved a $4.9 billion flood control bond in November, but this may not guarantee water security. Schwarzenegger has asked for a further $6 billion and wants a canal.
It is crucial that any scheme must protect the delta smelt, a highly endangered fish protected by law since 1993. Water flows from the delta were reduced to stop smelt being sucked into pumps.
Hanak believes some levees should be abandoned and farmers compensated.
Ultimately, says Wolff, California's "cultural mythology of abundance" will collide with limited resources, raising the question of sustainability. "It's a society that runs on cheap water, just like it runs on artificially cheap oil."
In a region where the hissing of sprinklers on summer lawns is regarded as a birthright, this reality has yet to sink in.
