In the past week, Northern California’s century-old Potter Valley Project crossed a major threshold toward dismantling. On July 25, PG&E submitted its formal plan to federal regulators to tear down the two-dam system that has rerouted Eel River water into the Russian River for over a century. Just days earlier, the Humboldt County Board of Supervisors became one of seven required signatories to a water diversion agreement, paving the way for a replacement system called the New Eel-Russian Facility, or NERF.

Together, the two developments mark a historic shift: The original infrastructure is on its way out, and the future of interbasin water sharing is up for grabs.

For more than 100 years, the Potter Valley Project has diverted Eel River water through a milelong tunnel blasted through a Mendocino County mountain, supporting agriculture, drinking water and firefighting from Potter Valley to Marin. Scott Dam, completed in 1922, created Lake Pillsbury to store the diverted water. 

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The South Fork of the Eel River, in Humboldt County, Calif.

PG&E now says the project is outdated, seismically vulnerable and economically unsustainable. Its decommissioning plan calls for removing both Scott and Cape Horn dams, eliminating the hydroelectric plant and draining Lake Pillsbury — triggering sharp debate across both river basins.

NERF, the proposed replacement, would divert water only during high winter and early spring flows, a major shift from the summer diversions that Russian River communities have long relied on. Eel River advocates say the timing is designed to protect salmon and restore ecological balance, but in the Russian River watershed, where steady summer water is critical........

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