Even in this, the wettest of years, the battle over endangered fish in the Sacramento-San Joaquin Delta rages.

The latest dispute centers on a plan by federal officials to increase water releases from Northern California reservoirs that eventually flow into the delta, where they hope to push encroaching salt water back to a point that is about 46 miles from the Golden Gate Bridge.

Four days of hearings began Tuesday before U.S. District Judge Oliver W. Wanger in Fresno, with water users seeking an injunction to stop the water releases.

The hearing will wrap up Friday. It is unknown whether Wanger will issue an immediate ruling.

Federal officials – supported by environmentalists – hope that reducing salt in a bigger stretch of the delta will help the threatened delta smelt. The action is part of a plan for the smelt known as a biological opinion.

But urban and agricultural water users that depend on the delta point out that Wanger has already invalidated the biological opinion, and in doing so specifically cited the fall water release as an area that needed reworking by the U.S. Fish and Wildlife Service.

Wanger's 225-page decision found that while delta pumping hurt the smelt, the restrictions that were set up to protect the fish were not justified. But in May, Wanger gave the federal government until December 2013 to rework the biological opinion, and left the existing plan in place while the new one is being written.

Court documents quote John Leahigh of the California Department of Water Resources as saying the proposed action will cut 850,000 acre feet of water deliveries to the State Water Project.

That, in turn, will cut State Water Project water allocations this year by 10% – about 410,000 acre feet – plus an additional 10% next year, state officials say.

Federal Central Valley Project water deliveries to the Westlands Water District and others will not suffer comparable reductions, court documents say, but could adversely affect water deliveries if conditions through the remainder of this year are "sufficiently dry."

Environmentalists, however, are "puzzled as to why the water contractors keep trying to stop fish protections in this wet year," said Kate Poole, an attorney with the Natural Resources Defense Council. "We're on target this year to export more water than ever before from the delta."

She cites water users' court filings that the proposed fall water releases won't hurt CVP supplies this year, and that there is a greater than 50% chance that it won't affect supplies next year.

Environmentalists also say state water allocation won't change this year, even if the fall action is taken, and that it is better than 50-50 that any reduction in the State Water Project's Lake Oroville for the increased fall water releases will be made up over the winter and spring.