It's not over yet. The Imperial Irrigation District has sued to halt a sweeping Colorado River drought plan that was signed in to law by President Trump on Tuesday. Officials with the sprawling, sparsely populated rural water district in southeastern California say the Salton Sea was wrongly left out of the plan.

IID holds among the oldest and largest rights to water from the river.

The petition, filed in Los Angeles Superior Court, alleges violations of the California Environmental Quality Act by the Metropolitan Water District of Southern California, and names the Coachella Valley, Palo Verde and Needles water districts as well. It asks the court to suspend the Lower Basin Drought Contingency Plan until a thorough environmental analysis has been completed.

“The logic in going forward without (us) was that the (drought plan) couldn’t wait for the Salton Sea,” Henry Martinez, IID general manager, said in a statement. “This legal challenge is going to put that logic to the test and the focus will now be where it should have been all along — at the Salton Sea.”

Martinez said in an interview that the district also had to act because of the continuing threat of possible mandatory water cuts, especially to farm districts like IID, if Metropolitan and others can't meet their obligations. MWD committed to keep 2 million acre feet of water in the reservoirs under the plan, and its general manager, Jeffrey Kightlinger, has said his staff concluded this year's healthy precipitation meant they could do it.

But Martinez said that was a short-term fix. "When you go through a drastic drought, you have to keep cutting back and cutting back. It is our opinion that Met cannot supply all of the water ... that would be required," he said. If mandatory cuts were ordered, "politically, urban water users are the heavyweights at the end of the day. ... Humans will beat out plants."

IID's petition alleges that MWD wrongly committed to enter into agreements on behalf of itself and all other California contractors.

In a statement, Kightlinger said, "We are disappointed that the Imperial Irrigation District is using litigation as a tool to block implementation of the Drought Contingency Plan. Parties on the Colorado River need to collaborate during this time of crisis, not litigate.”

The Colorado River and its reservoirs experienced 19 years of drought and, despite healthy snow pack and rains this year, experts predict climate change and overuse will continue to reduce flow levels. The system provides water for 40 million people and 5 million acres of farm land across seven western states.

U.S. Bureau of Reclamation, state water officials and others negotiated for six years to develop voluntary contingency plans if the reservoirs drop to preset levels. IID voted in December to sign on, provided it got the last say and that a pledge of nearly $300 million in federal funds was made to match state funds to shore up the Salton Sea. That didn't materialize, though federal and state officials are pushing to have funds allocated from the 2018 Farm Bill.

The Salton Sea, California's largest water body, has also been drying rapidly since January 2018, when Colorado River runoff from farms was diverted instead to urban San Diego and suburban Riverside County. Fish and migratory bird populations have crashed and potentially toxic clouds of dust could rise from the exposed lake shore.

IID was cut out of the drought plan after MWD stepped in and said it would contribute its rural neighbor's required share of water in drought years. The districts had previously signed contracts technically making the swap possible.

In his statement, MWD general manager Kightlinger said, “During our negotiations on the Drought Contingency Plan, it was our goal to find an approach that had no adverse impacts on the Salton Sea. That goal was achieved — the contributions to Lake Mead that will be made by Metropolitan and others will not decrease water going to the sea."

Reclamation and state water officials, including California, signed a joint letter to Congress requesting the drought plans be approved on March 19, without IID. The legislation passed rapidly and overwhelmingly, and was signed into law by Trump on Tuesday. Mexico will also be a party per a previous agreement. State representatives now need to finalize their approvals.

The ripples of IID’s lawsuit were felt in the Arizona legislature on Wednesday, where top water officials gave an update on the drought plan to the Senate Committee on Water and Agriculture. Arizona Department of Water Resources Director Tom Buschatzke testified that although the potential impact of the lawsuit was unknown, he doesn’t see it affecting much. He is encouraging more dialogue to bring IID back into the deal.

“They’re choosing right now to go down this path, but from my perspective, this will not prohibit us in moving forward and signing the Drought Contingency plan," he said.

Buschatzke said the focus is on implementing the Drought Contingency Plan as is. If MWD doesn’t sign as a result of the litigation, others will “assess where we’re at” then.

IID's Martinez said that the timing of the lawsuit the same day as Trump signed the legislation was coincidental. The district was up against a deadline to act once Metropolitan's board voted to approve taking on IID's share of water, he said.

More:LA offers to supply water instead of IID to get Colorado River drought plan across the finish line

More:Western drought deal is a go, without IID and as Salton Sea clean-up remains stalled

More:Top fed backs IID push for Salton Sea Farm Bill clean-up funds, with no linkage to drought plan

California law requires state and local agencies to identify significant environmental impacts of their actions and to avoid or mitigate those impacts if feasible.

Federal and MWD officials said that they had determined no harm would be done to the Salton Sea as a result of the plans. But IID officials and some observers said that's just half the equation.

"The district maintains that the Salton Sea is an integral part of the Colorado River system and its decline presents a severe public health and environmental crisis for the Imperial and Coachella valleys and the state," IID said in a news release on Wednesday.

Some agree with IID on the need to help the Salton Sea, even though they're on opposite sides on the lawsuit. They say IID could also play a key role in restoring the lake by signing easement agreements to allow restoration projects to begin. Martinez said the district was working on that and making progress.

Peter Nelson, a farmer who heads the Colorado River Board of California and who is a director of the Coachella Valley Water District, said of the lawsuit, "it's not totally unexpected but it's a bit disappointing."

He noted that IID and state water officials have battled over access across district land to build marshes that could suppress dust and help wildlife. Nelson said "from a state perspective, moving forward on the Salton Sea, it's my hope that IID and the state of California can resolve the easement issues. ... and move forward to develop habitat, which will also have a positive impact on air quality."

But he said that shouldn't let other states and the federal government off the hook. "From a federal perspective, I'm hoping that the Colorado River basin partners can rally around the 2018 Farm Bill efforts, which could help match" state funds.

Some water experts sympathized with IID, too.

"I'm a little bit frustrated that Imperial seemed to be on board (for years) and their attitude changed at the last minute to be more sensitive to the Salton Sea," said John Fleck, director of the University of New Mexico water resources program. "But I will say that from the perspective of the rest of us in the Colorado River basin ... whatever the outcome on the litigation, we as a community need to pay more attention ... because if we are solving this on the backs of residents of the Imperial Valley and the Coachella Valley, that's just wrong."

Janet Wilson is a senior environment reporter at The Desert Sun. She can be reached @janetwilson66 or at janet.wilson@desertsun.com

Arizona Republic reporter Andrew Nicla contributed to this report.