The question has also gone to the Legislature, with California Senate Bill 1 requiring the federal government's actions on water to comply with the state's Endangered Species Act. You can read more here, including how some federal environmental officials feel caught in the middle between the state and the White House.
Newsom's focus on protection hasn't gone unnoticed. In this commentary by Don Nottoli, a Sacramento County supervisor and chair of the Delta Counties Coalition, and Bill Dodd, a CA senator representing the Delta, Newsom is praised for rejecting the twin tunnels proposal and thereby calling for a more thoughtful process to conserve water and preserve the Sacramento Delta while also addressing irrigation needs. They praise Newsom's openness to "a more holistic approach that could include alternatives like water use efficiency measures, levee restoration, additional storage and other local projects supported by the Delta Counties Coalition."
They note that while the two-tunnel project was rejected, a single tunnel plan is still on the table, though its impacts have not been studied and there are no details about its size, location, cost or operation. What is certain, though, is that a tunnel alone won't be a sustainable solution for California water needs. "The funds allocated for tunnels would be better spent on regional portfolio-based measures, including strengthening levees, restoring ecosystem habitat, increasing water use efficiency, developing local and regional water supplies, and providing additional surface and groundwater storage and recharge." they write. "This winter’s storms underscore how much excess runoff we could have captured for future droughts and retained if we had more reservoir and groundwater recharge projects completed."