Body mass data (measured in grams) of dabbling and diving ducks harvested in three regions of California: Sacramento Valley, Suisun Marsh, and San Joaquin Valley during the 2014/2015, 2015/2016, 2016/2017, 2018/2019, and 2019/2020 hunting seasons. In addition to mass, the flattened length of right wing, species, sex, age, and date of harvest were also recorded. These data support the following publication: Herzog, M.P, Ackerman, J.T., Kohl, J.D., Fettig, B.L., Hartman, C.A., Peterson, S.H., Casazza, M.L., and Fleskes, J.P., 2024. Body mass changes of dabbling and diving ducks wintering in California. Journal of Wildlife Management, e22650. https://doi.org/10.1002/jwmg.22650