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WASHINGTON — For years, the Interior Department resisted proposals to raise the height of its towering Shasta Dam in Northern California. The department’s own scientists and researchers concluded that doing so would endanger rare plants and animals in the area, as well as the bald eagle, and devastate the West Coast’s salmon industry downstream.

But the project is going forward now, in a big win for a powerful consortium of California farmers that stands to profit substantially by gaining access to more irrigation water from a higher dam and has been trying to get the project approved for more than a decade.

For much of the past decade, the chief lobbyist for the group was David Bernhardt. Today, Mr. Bernhardt is the Interior Secretary.

It is not the first time that the Interior Department under Mr. Bernhardt’s leadership has taken actions that benefit his former client, the Westlands Water District, a state entity created at the behest of, and largely controlled by, some of California’s wealthiest farmers. Mr. Bernhardt also promoted the weakening of an endangered-species regulation that would get Westlands more water, a move that has put him under scrutiny from his department’s inspector general.