From – Two centuries ago, the floor of the Central Valley was largely a marshy wetland. In the springtime, the snowpack would melt, swelling the rivers beyond their banks and casting young fish out onto the floodplains where they would stay for months, fattening up on the abundant zooplankton and invertebrates until the floodplains drained, signaling the time to migrate to the ocean. However, the construction of levees – needed to control flooding of homes and farmland – also separated the rivers from their floodplains, denying access to native fish who have evolved to take advantage of floodplain habitat. (more).