California

... and by big agriculture because the tunnels would have put a hard upper limit on the capacity to send water south.

In the current system the amount of water sent south is ultimately limited by salt water intrusion. If the system was run at full capacity polluted drainage water and sea water would be drawn all the way to the pumps, further damaging fresh water environments and local water supplies.

Many California farmers and developers don't want ANY fresh water to flow into the ocean. If they could capture all the fresh water they would, the natural environment be damned (and dammed too.) Then they'd take Oregon's water.

This new tunnel design would impose even greater limits on the amount of water that could be withdrawn and sent south, which is good for the little that remains of the Delta's natural environment, but opposed by developers and farmers who would take every last drop of fresh water if they could. They hate Newsom, they consider any water that flows into the ocean wasted, and post signs along the highways saying so.