What, you may ask, is the "spring flush?" In late spring and early summer, large concentrations of herbicides are flushed from croplands. These chemicals — like the herbicide atrazine — then get transported far and wide through surface water systems.
Herbicides are water-soluble and thus have the potential to leach into groundwater supplies as well as streams, lakes and other surface waters. Atrazine is a frequently found contaminant in drinking water supplies throughout the Corn Belt, and every year the spring flush raises concerns over the potential of atrazine spikes in drinking water supplies.