The Sacramento-San Joaquin Delta ecosystem was once a very different place. Before levees and dams, the rivers and streams that flowed through the Central Valley into the San Francisco Bay swelled and shrank with the seasons. Huge, shallow floodplains warmed by the sun mingled with icy mountain snowmelt to create a habitat rich with microscopic plankton, the base of the aquatic food chain. Now, nearly all the waterways that feed the Delta are channelized for shipping, farming and flood control, none more so than the Sacramento River.