Pesticides (herbicides and insecticides) are used extensively in the White River Basin. Application of herbicides is done during the spring planting months to virtually the entire corn and soybean crop. The herbicides most frequently detected in the White River during 1991-95 were the triazine (primarily atrazine and cyanazine) and Acetanilide (alachlor and metolachlor) compounds. The highest concentrations of herbicides in the river were typically found during late spring runoff following application. Generally, concentrations of alachlor have been decreasing, while concentrations of acetochlor have been increasing, in response to changes in the use of these herbicides in the basin. The total amount of the commonly used herbicides transported by the river is about 1 percent or less of the amount applied to cropland. Insecticides commonly used in urban and agricultural areas also were found but in much lower concentrations than commonly used herbicides.

Geist Reservoir Atrazine Concentrations