Assessing the Effect of Pesticides in Agricultural Runoff on Aquatic Life in the Sangamon River Near Monticello, Illinois

Stream-water samples collected from a midwest stream, following a thunderstorm during May 1991 were toxic to water fleas ( Ceriodaphnia dubia ), but not fathead minnows ( Pimephales promelas ), or a bacterium ( Photobacterium phosphoreum ) or green alga ( Selenastrum capricornutum ). It was unlikely that the toxicity to the water fleas was caused by herbicides, but it may have been caused by insecticides.