It's easy to say the just-released new look at Sacramento-San Joaquin Delta water flows is "immaterial" -- which a prominent irrigation district official did last week.

We have different advice for California irrigators and cities that look to water exports through the Delta: Ignore this study by the state Water Resources Control Board and California Environmental Protection Agency at your peril.

The study, under way for nine months and now released in draft form, finds that a lot more fresh water needs to pass downstream during certain months of the year if eight aquatic critters, from Chinook salmon to zooplankton, are to be sustainable.

This report is the foundation for a lot more scientific looks at a variety of issues as the recently minted Delta Stewardship Council grapples with a long-range strategy envisioned by the 2009 Delta Reform Act. The law was part of a package of water bills that cleared the Assembly last year.

The Water Board worked on the narrow concept of protecting the public's interest in waters of the state.

Public trust, or stewardship of a shared resource, has a big place in the Golden State. The California's Supreme Court in 1983 took a liberal interpretation of the public trust. Invoking that trust can be the basis for modification of existing water rights.

Water users -- and Delta Stewardship Council members --must keep the stakes and the law in perspective. Those stakes are high indeed, not just for them but for the public.

Water used by more than two-thirds of Californians flows through a network of waterways run by state and federal agencies. That same system delivers irrigation water to about 2 million acres of farmland, including some of the nation's most productive cropland.

Dismissing a 191-page report -- which concludes that from January to June each year 75 percent of the "unimpaired" outflow of the Delta is needed in the San Francisco Bay estuary -- isn't advised. Unimpaired is water talk for natural flows that occur if there's no diversion, storage or flood control structures in place on a watercourse.

In the past two decades, discharge from the Delta has been as low as 30 percent of unimpaired outflow in dry years all the way up to almost 100 percent in the wettest ones.

Consider this: If 75 percent outflow is what it takes for healthy habitat, water users in the upper tributaries of both the Sacramento and San Joaquin basins may face alteration of historic water rights and storage plans. This would occur if the Water Board attempts to strike a balance between the public trust and current operations that include massive interbasin transfers of water.

One paper before the Water Board report warns that "it is highly unlikely that any fixed or predetermined prescription will be a 'silver bullet.' The performance of native and desirable fish populations in the Delta requires much more than fresh water flows."

Indeed, more fresh water isn't likely to be the silver bullet. But a reasoned, science-based look can't be ignored.

At the very least this should trigger a re-examination of the Water Board's D-1641, the policy that sets the bay and Delta flow requirements now in use. It was written 15 years ago.

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