In 1991 a study of two urban streams in Hamilton and two urban stormwater detention ponds in Guelph was initiated to detem1ine the degree of pesticide contamination in these systems. Water was tested for phenoxy acid herbicides (i.e. 2,4-D, mecoprop, dicamba, MCPA), for neutral herbicides (i.e. trifluralin, atrazine, metolachlor), and for organophosphorus insecticides (i.e. diazinon, dimethoate, chlorpyrifos), during base flow and during runoff events. Sediment was collected and analyzed for persistent organochlorine compounds and for selected pesticides. A questionnaire was circulated to the residents of two Guelph subdivisions to determine the types and amounts of pesticide used by householders. Canadian Water Quality Guidelines (CWQG) for Drinking Water were not exceeded for any of the pesticides. Concentrations of 2,4-D did exceed the