The Sacramento and the San Joaquin rivers flow west out of the Sierra Nevada forming the Delta, the labyrinthine skein of water and wetlands that have for centuries of centuries been the living source of the San Francisco Bay. Now no more.

The freshwater yield of the Sierra’s snowmelt once surged through the delta and out the Golden Gate, creating a fluctuating brackish zone that sustained a vast food web, from plankton to the once-ubiquitous, now nearly extinct delta smelt, to salmon and steelhead. But with the completion of the government projects, the water went through home taps and San Joaquin Valley irrigation canals instead; the essential biological productivity of the delta wavered, and then dipped.

Through the years, the decline steepened, ultimately becoming a free fall. Adding to the stress of fresh water diversions were other factors: the maceration of fish by the huge pumps that send water south from Tracy; the introduction of exotic fish, mollusks, crustaceans and plants that competed with native species; and toxic runoff from agricultural operations.

The delta is now in its endgame. It is no longer, in fact, a true delta. Two great rivers still meet east of Suisun Bay, but the phenomenally rich wetland they created is, for the most part, gone. A maze of “islands” bordered by stagnant sloughs and canals exists in its stead. Buttressed by frangible earthen levees, these agricultural tracts have subsided from decades of compaction and soil oxidation; on some of the islands, tractors churn the peat soils 20 feet below houseboats and water skiers plying the sloughs just beyond the levees. One good quake on the nearby Hayward Fault and the levees would liquefy, during the region into a great inland bay.

Read Glen Martin’s fine report in the SF Chronicle Magazine.