Ponded Poisons

It seemed like a good idea to the U.S. Bureau of Reclamation. The state of California requested the federal construction of a major channel to transport subsurface water away from the agricultural fields irrigated by the BOR's Central Valley Project. San Joaquin Valley farmers could not let the water table, made shallow by impermeable underlying clay layers, build up and inundate the roots of their crops.

BOR purchased 5,900 acres of grasslands and by 1972 had constructed an 82-mile concrete-lined channel. It led to a reservoir consisting of 12 evaporation ponds on 1,280 acres. The overlay Kesterson National Wildlife Refuge was established in 1970. Peak populations of 12,000 wintering waterfowl were observed on the water-filled ponds with many more on the surrounding habitat. The reservoir was planned to ultimately cover a 4,700-acre area with an eventual discharge into the valley's river system. But that never happened.

In 1981, San Luis NWR complex manager Zahm sensed something was wrong. Routine tests indicated high selenium content in the pond water. Selenium is a trace element present in alkaline desert soils. But impacts of it were not observed in wildlife until 1983. That's when both deaths and deformities of newborn birds began: complete absence of eyes, malformed legs, wings, and mandibles, and high mortality among coots, grebes, stilts, and ducks. Investigators learned that, as the water evaporated, the selenium and other minerals and salts were being left behind, accumulating in the ponds and entering the food chain at toxic levels.

The tragic results caught the attention of the public. BOR and refuge personnel tried to frighten birds away by using exploders and fireworks. Nearby habitat was flooded with fresh water in an effort to lure them from the poisoned evaporation ponds.

The attempts were ineffective. Lawyers warned that continued losses from selenium ingestion could be a violation of the Migratory Bird Treaty Act.

Department of the Interior officials decided there was no alternative but to plug the drain and fill in the reservoir. Delivery of drain water ceased in 1986, and the ponds were buried under clean fill in 1988. Except for the reservoir area, 4,460 acres of the Kesterson Project were transferred from BOR ownership to the refuge in 1992. Agricultural drainage is now routed to the San Joaquin River where it is diluted as it moves toward the Sacramento-San Joaquin River Delta and the Atlantic Ocean.

For more information:
San Luis NWR Complex, P.O. Box 2176, Los Banos, CA 93635, 209-826-3508.

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