The Kesterson National Wildlife Refuge is an artificial wetlands environment, created using agricultural runoff from farmland in California's Central Valley.

The irrigation water is transported to the valley from sources in the Sierra Nevada mountains via the California Aqueduct. Minerals from these sources are carried in the water and concentrated by evaporation from aqueducts, canals, and fields, which has resulted in an accumulation of selenium and other minerals in the wetlands. Wildlife in this region suffered deformities due to selenium poisoning, drawing the attention of news media and leading to the closure of the refuge.