A figure is enough to summarize the disaster: 64%. This is the rate of malformation or mortality observed among embryos and hatchlings at the Kesterson National Wildlife Refuge in California, just two years after agricultural drainage water began being discharged into its basins. The problem peaked in 1983, when 64% of embryos and hatchlings of wild aquatic birds in the refuge's ponds showed severe deformities or died. The U.S. Geological Survey gave this phenomenon a name: "the Kesterson effect." The issue originated with the San Luis Drain, a proposed 290-mile drainage canal designed to carry surplus agricultural water from the San Joaquin Valley to the ocean. However, only 85 miles of the canal were completed, and this unfinished section ended up directing water into the basins of the Kesterson National Wildlife Refuge. Selenium, a naturally occurring element found in sedimentary rocks, became concentrated in the refuge's closed basins due to evaporation. When aquatic birds were exposed to high levels of selenium, their embryos and hatchlings were born with severe deformities, including malformed beaks, missing wings, and unformed skulls. The problem has persisted for 35 years, as selenium continues to circulate through the agricultural soils of the San Joaquin Valley during irrigation. The refuge, originally intended as a sanctuary for wildlife, was turned into an unintended disposal site for agricultural runoff. Despite warnings from the California Department of Water Resources and biologists from the U.S. Fish and Wildlife Service, the project proceeded. In 1975, funding for an alternative drainage system was cut, leading to increased toxic discharges into the Kesterson basins. Selenium is not an industrial contaminant; it is a naturally occurring mineral found in marine sedimentary rocks from the Cretaceous period. In the San Joaquin Valley, irrigation water dissolves selenium from the soil, carrying it into drainage systems. Evaporation in the closed basins of the refuge concentrates the selenium, which then accumulates in the food chain. By 1983, the effects were visible: newly hatched birds had grotesque deformities, including eyeless eggs and missing wings. A 1984 photograph showed a pied-billed grebe with severely deformed legs, a vivid representation of the impact of selenium contamination. Selenium levels in adult birds at Kesterson were ten times higher than in a control group, and in their eggs, they were twenty to thirty times higher. This explains why embryos and hatchlings suffered the most, as they were exposed from the formation of the egg to concentrated doses of the toxin. Faced with the extent of the damage, California authorities took action. In 1985, the State Board issued orders to stop the flow of contaminated water and to refill the basins with fresh water. The existing 85-mile section of the San Luis Drain was closed in 1986 after further deformities were found in birds. However, a 28-mile section of the canal now carries drainage from 100,000 acres to the San Joaquin River. Despite these measures, selenium continues to be detected in bird eggs at other agricultural sites in the region, indicating that the "Kesterson effect" is not an isolated incident but a persistent geochemical process that occurs whenever intensive irrigation meets selenium-rich soils.