California Gov. Jerry Brown is set to announce plans for building a massive twin tunnel system to carry water from the Sacramento-San Joaquin River Delta to farmland and cities. The announcement is expected Wednesday. The $23.7 billion proposal also includes plans for more than 100,000 acres of floodplain and tidal marsh habitat restoration. Opponents say the tunnels will further harm the ailing delta ecosystem, increase costs for water users and devastate the area's agricultural-based economy. Supporters say the project will guarantee a steady water supply for Californians and will help fish species - though officials acknowledge the impacts of reduced flows and habitat restoration on fish remain unknown. Officials say the amount of water diverted will depend on results of scientific studies that will accompany construction.