STOCKTON - Someone must make a hard decision about how to fix the Delta, a decision that will likely involve trade-offs, a Stanford University professor of civil engineering told alumni and community leaders on Wednesday.

Delta smelt are "definitely on the way out," Stephen G. Monismith said during a luncheon address, while other species such as striped bass and salmon also have declined.

Changes to the state's water delivery system - such as a peripheral canal, the "$10 billion experiment" - may not be enough, he said.

"We seem to be getting more and more questions," Monismith said. "I wish it was as simple as re-plumbing the Delta."

A key issue, he said, is how much fresh water flows through the Delta and out into San Francisco Bay.

When flows are high, saltwater is pushed back to the west; during low flows, salt creeps into the Delta and potentially affects the amount of food available for fish, not to mention water quality for farmers.

He said a holistic approach to the Delta is needed, rather than considering its many parts piece by piece.

"At least people are starting to think about what we want the Delta to be," he said.

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