President Trump on Wednesday signed a memorandum directing more of California’s scarce water supply to farmers and other agriculture interests in the state's Central Valley, a Republican stronghold.

Speaking alongside House Minority Leader Kevin McCarthy in the lawmaker’s hometown of Bakersfield, Trump boasted of how his administration reworked environmental rules to assure more water gets to farmers, while also taking shots at his political rivals – from California Gov. Gavin Newsom to Democratic presidential primary hopeful and former New York City Mayor Mike Bloomberg.

“For too long water authorities have flushed millions of gallons into the Pacific,” Trump said. “I ordered the administration to update outdated opinions which determined water allocation in this state.”

Trump added that he is going “to put a lot of pressure” on Newsom to enact the changes and if the California governor doesn’t follow through then “you’ll get a new governor.”

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Trump has long criticized the environmental rules governing the flow of water in California – calling the rules “insane” during a campaign stop in 2016 and pledging that he’d be “opening up the water” for farmers.

The environmental rules are meant to ensure that enough water stayed in rivers and the San Francisco Bay to sustain more than a dozen endangered fish and other native species, which are struggling as agriculture and development diverts more water and land from wildlife.

Environmental advocates and the state say the changes will allow federal authorities to pump more water from California's wetter north southward to its biggest cities and farms.

The Trump administration, Republican lawmakers and farm and water agencies say the changes will allow for more flexibility in water deliveries. In California's heavily engineered water system, giant state and federal water projects made up of hundreds of miles of pipes, canals, pumps and dams, carry runoff from rain and Sierra Nevada snow melt from north to south — and serve as field of battle for lawsuits and regional political fights over competing demands for water.

Environmental groups say the changes will speed the disappearance of endangered winter-run salmon and other native fish and make life tougher for whales and other creatures in the San Francisco Bay and Pacific Ocean.

After an initial study by federal scientists found the rule changes would harm salmon and whales, the Trump administration ordered a new round of review, California news organizations reported last year.

The overall effort “ensured the highest quality" of evaluation of the rule changes, Paul Souza, Pacific Southwest director for the Fish and Wildlife Service, said in a statement Tuesday.

“We strongly disagree that the proposal will reduce protections for endangered species," Souza said.

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Beyond operational changes in the federal Central Valley Project water system, the administration's changes allow for more habitat restoration, upgrades in fish hatcheries and the water system itself, monitoring of species and other improvements, Souza said.

Conservation groups have promised new rounds of lawsuits to try to block the redone environmental rules.

“The species really are in much worse shape” than in earlier years, Doug Obegi with the Natural Resources Defense Council said. “We are at the point where we may watch them wink out ... potentially in the next few years.”

Fox News' Morgan Phillips and The Associated Press contributed to this report.