By Bettina Boxall / Los Angeles Times

LOS ANGELES — Federal fishery agencies Monday pushed forward a controversial water project that would change the way Northern California supplies are sent to Southern California.

The U.S. Fish and Wildlife Service and the National Marine Fisheries Service concluded that the construction of new diversion points on the Sacramento River and two massive water tunnels would not jeopardize the existence of endangered species in the Sacramento-San Joaquin Delta, which is the hub of California’s water works.

The release of the documents marks a major — but by no means final — step in the long, twisting path of the proposal, which has been in the planning stages for more than a decade.

Called biological opinions, the reviews lay out the endangered species protections that will determine how the tunnel project is operated — and thus how much water it can divert to the big delta pumps that send water south to San Joaquin Valley agriculture and Southern California cities.

The agencies that get supplies from the delta will scrutinize every line of the opinions before they decide whether to fully commit to funding the $15 billion project.

The question for the Metropolitan Water District of Southern California, Westlands Water District and others will be whether the tunnels stabilize their delta deliveries enough to justify the cost.

If they decide it doesn’t and withdraw their support, the proposal will die.

But even if the districts give the thumbs up, the tunnels still need several state and federal permits before construction can begin. And opponents are expected to challenge approvals in court, which could stall the project for years.

Delta growers vehemently oppose the tunnels, which would require years of disruptive construction in their backyards and suck up good quality fresh water before it reaches their irrigation ditches.

Environmentalists argue the tunnels will inevitably be used to send more water south, further depleting flows vital to the delta’s faltering ecosystem.

Dubbed the California WaterFix by the state, the proposal calls for construction of a new diversion point on the Sacramento River in the north delta, along with two massive underground tunnels that would carry water 35 miles to existing government pumping plants in the south delta.

The powerful pumps now draw entirely from the south delta, causing delta channels to flow backwards and pulling imperiled native fish to their deaths. That triggers endangered species protections that limit pumping, cutting delta deliveries.

By reducing withdrawals from the south delta, the new diversion points would lessen the reverse flows and — backers hope — loosen the pumping restrictions.

In draft reviews, federal biologists were consistently skeptical of the proposal. They warned that taking large amounts of fresh water from the north delta will create a new set of problems for migrating Chinook salmon and the vanishing delta smelt.

The U.S. Fish and Wildlife Service found that construction and operation of three new river intakes and the twin tunnels would destroy smelt habitat that will become increasingly important as climate change and sea level rise alter delta conditions.

The National Marine Fisheries Service concluded that as far as winter-run Chinook salmon are concerned, the new diversion would change river flow patterns and temperatures for the worse, hurting overall survival of the endangered species.