There are many dams and gigantic underground pipes that carry the water through the area. It works fine for the water but not for kayakers. For example the Brio

There are many dams and gigantic underground pipes that carry the water through the area. It works fine for the water but not for kayakers. For example the Briones Reservoir is upstream of the San Pablo Reservoir connected by huge gravity-powered pipes under the mountains between them. They are in fact redoing them right now.