SEATTLE - A new report warns that much of King County's economic base could be crippled in a big flood.

Manufacturing, aviation and some of the county's highest paid jobs are all located in flood plains, and one of the only things protecting them is an aging levee system.

Where once the Green River meandered through rich King County farm country, it now weaves its way through one of the county's richest economic districts.

"There's billions of dollars in assessed valuation down here and it drives the economy of King County in many ways," said Steve Bleifuhs, of King County flood management.

That's why county leaders are putting levee repair projects on the fast track. They know a flood could cripple that economic engine and the new study only amps up the concern.

The independent report, prepared by ECONorthwest, Inc., breaks down the flood plain economy this way: It's home to some 65,000 jobs that produce wages 13 percent higher than the county average. Workers bring home an estimated $3.7 billion dollars a year a year from the flood plain.

The old levees, no longer recognized by FEMA as protection from a catastrophic flood event, are all that defend an estimated $43 million-a-day economy.

On some days the Green River looks gentle and harmless, but just last year the level was just a few feet away from unleashing economic damage.

Flood waters inundated several residential areas in that flood, but the levees held in the industrial zones. Still experts know floods are as inevitable as the falling autumn leaves - they just hope to get this system fixed before the big one.