The State Water Resources Control Board last week issued a draft report that concluded what has long been obvious – excessive diversions of water are imperiling the Sacramento-San Joaquin Delta and the fish that depend on this estuary.

This is hardly a shocker. Over the last several decades, cities and farms have diverted about 50 percent of the flow of the Sacramento River and nearly two-thirds of the San Joaquin River.

It doesn't take a rocket scientist (or a fish scientist) to tell you that fish need water – preferably cool, unpolluted water. If you take that water away, or return it to the river laden with fertilizers, pesticides and higher temperatures, fish suffer. It is that simple.

Defenders of the status quo are already attempting to discredit the state board's findings and mislead the public about next steps. U.S. Rep. Jim Costa, a Fresno Democrat who faces a tough re-election bid and is trying to burnish his standing with corporate farmers, lambasted the report as one-sided. "This kind of misinformation serves as fodder for extreme environmentalists and critics of our valley who aim to cut off our water," he told reporters.

This is ridiculous.

Last year, the Legislature approved a sweeping overhaul of state water law aimed at twin goals – improving water reliability and restoring the Delta. The package was controversial. Many in Northern California called it a water grab. One reason The Bee supported it was because it included provisions, sought by Environmental Defense Fund and other groups, that the state board examine the flow needs of the Delta and ensure that those needs were considered in any attempt to alter water conveyance in the estuary.

The state board's draft report responds to that directive, but it is not the last word on how the Delta will be managed. It doesn't mean that stressors such invasive species and poorly treated sewage are non-factors in the Delta's decline. Nor does it mean the state will seek to return the Delta to pre-18th century conditions. The Delta faces competing interests, and any attempt to restore it must recognize that the clock cannot fully be turned back.

Yet science must to play a part in any effort to replumb the estuary. The state board's report is a step in that direction.

The needs of fish need to be known and accepted. The desires of powerful water users are already known. Reconciling the two will be the challenge.