Before the Sacramento River was leveed and confined in the late 1800s, its winter floods spilled across vast floodplains, creating warm, food-rich shallow water where juvenile Chinook salmon grew quickly before heading to the ocean. Today, only about 5% of that original Central Valley floodplain habitat remains, and the loss of that nursery ground is one of the biggest reasons salmon struggle to reach the size and strength they need to survive their ocean migration.

The Nigiri Project, launched by CalTrout, UC Davis's Center for Watershed Sciences, the California Department of Water Resources, the California Department of Fish and Wildlife, NOAA's Southwest Fisheries Science Center, the U.S. Bureau of Reclamation, and private landowners Knaggs Ranch and Cal Marsh and Farm Ventures, tests a simple idea: farmland in the Yolo Bypass sits fallow all winter anyway, so why not flood it and let it function as the historic floodplain it once was? In its original 2012-13 pilot on Knaggs Ranch, the project reared 53,000 juvenile salmon across just 25 harvested acres, and the results exceeded expectations: fish gained weight fivefold in six weeks, growing from 0.92 grams to 6.45 grams, among the highest growth rates ever recorded in Delta salmon research.

Follow-up research from UC Davis has continued to confirm why: zooplankton, the tiny invertebrates juvenile salmon feed on, are 53 to 150 times more abundant in these flooded rice fields than in the adjacent river channel, and fish raised there grow two to five times faster than fish in the Sacramento River itself. That science has since scaled into a broader vision: up to 2,500 acres of winter floodplain habitat in the Yolo Bypass, managed to maintain flood control capacity while improving fish passage, reducing juvenile stranding, and boosting outflows that feed the wider Delta food web. The Nigiri Project's findings now directly inform CalTrout's larger Fish Food on Floodplain Farm Fields program, which has taken this same concept and scaled it across tens of thousands of acres of Central Valley rice fields.