San Francisco Mayor London Breed delivered a surprising veto on Friday against the Board of Supervisors’ unanimous vote on Tuesday for a resolution supporting the state’s controversial new Bay-Delta plan.

The plan would require rivers in the San Joaquin Valley to maintain an average of 40% of “unimpeded flow” during the spring months. That would take water from farmers — and also from San Francisco, which relies on the watershed.

Some 85% of the water used by San Francisco and its suburbs comes from the Hetch Hetchy Reservoir on the Tuolumne River, which is the waterway most likely to be affected by the Bay-Delta plan. San Francisco’s Public Utilities Commission (PUC) opposes the plan, as do farming interests and communities in the Central Valley. But environmentalists and fishing interests support the plan, which they hope will revive native fish populations.

The State Water Resources Control Board (SWRCB) will hold a final vote on the plan on Wednesday, November 7 — conveniently, one day after the midterm elections. Several Central Valley politicians of both parties — especially Republicans, and notably Rep. Jeff Denham (R-CA) of the 10th congressional district — have vigorously opposed the Bay-Delta plan, calling it a “water grab.”

Denham has attacked his Democratic opponent, Josh Harder, for failing to show up at an August rally against the Bay-Delta plan (though Harder later said that he opposes the plan).

The San Francisco Board of Supervisors had opposed the plan in an effort to send a message of protest to President Donald Trump.

But Breed had more practical concerns: “We all want the same outcome for the Bay-Delta — a healthy ecosystem that both supports fish and wildlife and provides reliable water delivery,” she said in a statement quoted by the San Francisco Chronicle. But “it is deeply irresponsible for San Francisco to take a position that would jeopardize our water supply.”

Joel B. Pollak is Senior Editor-at-Large at Breitbart News. He is a winner of the 2018 Robert Novak Journalism Alumni Fellowship. He is also the co-author of How Trump Won: The Inside Story of a Revolution, which is available from Regnery. Follow him on Twitter at @joelpollak.