Test species include the larval fathead minnow, Pimephales promelas (less than 24 hours old), the cladoceran, Daphnia magna (10-d old) and the alga Selenastrum capricornutum (4-7 d old). The test species were selected for their sensitivity to selenium, diazinon and chlorpyrifos and tolerance of usual water quality of the study area. Fathead minnows are sensitive to selenium; Daphnia magna is sensitive to pesticides; the algal study will include a bioaccumulation component.