SACRAMENTO, Calif. -- The Sacramento-San Joaquin Delta ecosystem, particularly endangered fish species, could benefit from California Gov. Jerry Brown's $23 billion proposal to build two massive tunnels to move water from Northern California to farms and cities in other parts of the state, according to the second piece of his plan released Wednesday.

Environmentalists and others, however, remain skeptical, saying it's essentially the same plan as before but with more chapters.

Chapter 5 of the "draft Bay Delta Conservation Plan" detailed what impact the tunnels and subsequent changes to the estuary could have on the region's 57 native fish and wildlife species, particularly the endangered Delta smelt and Chinook salmon populations.

"At the beginning of the Brown administration, we made a long-term commitment to let science drive the Bay Delta Conservation Plan," John Laird, the state's secretary for Natural Resources, said at a news conference Wednesday. "Today, we continue to make that a reality as we drive toward a holistic resolution to bring the Delta back from the brink."

The other two chapters released Wednesday laid out a timeline for the plan's rollout, along with the responsibilities of various stakeholders in its implementation and governance. Construction could start as early as 2017 and be completed by 2026. The thousands of pages of scientific analysis, which looked at 68 different scientific models, are aimed at giving federal and state fish and wildlife agencies information to decide how and if they will authorize permits.

"An immense amount of science has gone into the (plan), but we know there will always be scientific uncertainty," said Charlton Bonham, director of the state Department of Fish and Wildlife. "The only thing for certain is that if we do nothing, things will get worse from a conservation point of view."

The plan must meet federal Endangered Species Act and the state's Natural Community Conservation Planning Act standards.

According to the plan, pumping water out of the Sacramento River farther north than the existing pumps in Tracy would benefit the Delta smelt. Plans call for creation of more than 140,000 acres of new habitat - floodplains, tidal marshes and grasslands - from existing Delta islands at a cost of about $4 billion to be footed by taxpayers.

Though there is some uncertainty, the plan says tidal wetlands restoration would increase the amount of suitable habitat and local food for consumption, while decreasing the number of smelt that get sucked into the pumps.

At a news conference Wednesday, the California Resources Agency said there would be significant improvements for the smelt during wet years, though during dry years, they would be killed at the same rate as today by existing pumps.

Some local groups, however, remain unpersuaded.

Barbara Barrigan-Parrilla, executive director of Stockton-based advocacy group Restore the Delta, doesn't buy the plan's rationale that the smelt population is going to increase. She further contends the state's "wild claim" will put local fisheries in jeopardy.

"The last draft (in February 2012) said that entrainment (by the Tracy pumps) would increase, and now they are saying it's going to decrease, but looking at the plans, they haven't changed anything," Barrigan-Parrilla said.

Janet McCleery, president of Discovery Bay-based Save the California Delta Alliance, agrees.

"The latest chapters contain nothing new, just several thousand pages of more of the same," she said. "The (plan) continues to ignore what the Legislature deemed as the starting point - identification of the amount of water that needs to flow through the Delta to maintain water quality and restore the fish populations."

These chapters continue to rely on the notion that habitat restoration areas are the answer for saving the fish, even though the current habitat restoration experiments in the Delta are not showing significant results, McCleery said.

"Regardless of how much acreage they plan to convert for habitat restoration, the fish will continue to decline as water quality degrades," she said.

The new plan is still consistent with the National Academy of Science's 2012 judgment that the effect analysis is just a rationale for building tunnels, Barrigan-Parrilla said.

State officials say the new version of the plan has been substantially modified from last February's draft, including a reduction in the number of intakes along the Sacramento from five to three, reducing the amount of water brought in by 40 percent.

Under Brown's plan, two side-by-side underground tunnels, each 40 feet high, would carry fresh water 35 miles from the state's largest river, the Sacramento, under the Delta to giant federal and state pumps near Tracy.

Supporters, including large urban water districts and farmers, say it will help the state's most important water source return to health and reliability after years of collapsing fish populations and court rulings limiting pumping.

Earlier this month, the state released the first four chapters of the plan: hundreds of pages of documents containing historic information about Delta species, an overview of the yearslong planning process and 22 conservation measures that planners said the tunnels project could help achieve.

The final three chapters, which lay out the project costs, are expected to be released in late April.

(Staff writer Paul Rogers contributed to this story.)

• Read more articles by PAUL BURGARINO

Order Reprint