The board of the Westlands Water District on Tuesday dealt a potentially fatal blow to the most ambitious California water project planned in decades. By a 7-1 vote, the state’s largest irrigation district decided not to join California WaterFix — a $17-billion plan to build two tunnels under the Sacramento-San Joaquin Delta that would re-engineer the way Northern California supplies are moved to the rest of the state. The proposed financing structure of the project “doesn’t work for Westlands Water District,” board member Todd Neves said.