Evaporation ponds used for agricultural purposes can resemble wetlands that are the natural habitat of waterfowl and migratory birds, and there are some inherent risks due to high concentrations of salts and trace elements in the drainage runoff. When farmers have no access to rivers or other means of drainage control, evaporation ponds used to contain runoff typically have a high salinity content and may contain trace elements such as selenium, a chemical with properties similar to arsenic. Among other possible effects, California officials cite the possible endangerment of the reproductive health of ducks. In addition, if dead bird carcasses are not removed promptly from such drainage ponds, there is an additional risk of disease spread, including avian cholera and botulism.
The Tulare Lake Basin in California has been used as a testing ground to study the effects on wildlife, and various state and national agencies, including the California Department of Fish and Wildlife, the U.S. Fish and Wildlife Service and local evaporation pond operators collaborate to develop better methods of dealing with agricultural drainage. The goal, of course, is to mitigate any adverse effects on local or migrating wildlife and to eliminate any risk to humans. Even though the California Central Valley Regional Board has a requirement that pond operators must “avoid, minimize and mitigate wildlife impacts” of evaporation ponds, there has been only limited success.
