The San Joaquin River's meandering course through central California would get steered in yet another direction under a far-reaching bill set for House approval this week.

Salmon would be out. Other fish would be in. One restoration program would end. Another would start. Water would flow below Friant Dam north of Fresno, but not nearly as much as currently planned.

Biologically, scientists say, the House proposal has promise. Politically, it faces strong opposition. Legally, it appears vulnerable to challenge. Bottom line: When the biggest California water bill in years hits the House floor, as it is expected to do Wednesday, the San Joaquin River will be incontrovertibly front and center.

"The San Joaquin River," chief bill author Rep. Devin Nunes, R-Visalia said, "is the lynchpin of the entire bill."

The river section spans nearly half of the 53-page Sacramento-San Joaquin Valley Water Reliability Act. The section is titled "Repeal of the San Joaquin River Settlement," though "repeal" does not really convey the consequences.

Instead, if the section survives, it would replace a cold-water fishery, in which salmon return to the San Joaquin River, with a less expensive warm-water fishery, conducive to other river-loving species.

"I think it's a reasonable thing to propose," said Doug Welch, natural resources planner with the Chowchilla Water District, which joined other farm water groups in agreeing to the current salmon plan. "The jury is still out on restoring a self-reproducing salmon run."

Elsewhere, the new House bill restores longer irrigation contracts, preempts strict state laws and eases water transfers. It offers more water for San Joaquin Valley farms, while painstakingly negotiated language is designed to ease Sacramento Valley fears about supplies being shipped south.

The overall bill sharply divides the state, and its long-term prospects are uncertain.

The bill's authors have rallied the public support of some 70 California water districts, 20 farm organizations and 20 cities and counties, among others.

"This treats our water as the precious resource it is, and restores balance between human and environmental uses of that resource," said Rep. Tom McClintock, R-Elk Grove, chairman of the House water and power subcommittee.

But 10 House Democrats from Northern California oppose the overall bill, as do the state's two senators and the administration of Gov. Jerry Brown. The House Democrats, who together represent about 7 million residents, say they were shut out of the months-long bill drafting that occurred under McClintock's oversight.

"Sacramento is concerned that this legislation would create chaos in the already challenged context of the Sacramento-San Joaquin Delta," said Sacramento City Council Member Jay Schenirer, adding that, "Sacramento has not been allowed to be at the table or to address its concerns."

The bill's San Joaquin River provision blocks a 2009 law, which Congress passed to implement a lawsuit settlement reached between environmentalists and Friant Water Users Authority farmers.

The settlement requires additional water to be released through Friant Dam, and for myriad river channel improvements, so salmon can be returned starting this year. The average releases would be about 200,000 acre-feet, about 15% of the total available.

The Nunes bill, by contrast, would send an estimated 100,000 acre-feet of water down the river channel, less than half of the river settlement's average. Supporters say a warming climate will make it more difficult for cold-water fish, such as salmon, to survive as far south as Fresno. Other native fish might do very well under the alternative warm-water plan, including trout, Sacramento sucker and threespine stickleback.