Sixteen different pesticides or their metabolites (degradations products) were detected in water samples collected in 1999 from three networks of lakes and reservoirs in upstate New York that are sources of public water supply. The networks sampled included the New York City network (10 reservoirs); the Finger Lakes -Great Lakes network (three Finger Lakes and two Great Lakes that supply large and small cities) and the western New York reservoir network (three reservoirs that supply small

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... or towns). The concentrations of the compounds detected in the samples generally were low. Only a few of the compounds detected had a concentration exceeding 1 µg/L (microgram per liter), and no compounds detected in the New York City reservoirs network had concentrations exceeding 0.05 µg/L. None of the compounds detected exceeded any Federal or State water-quality standard. Compounds that were most frequently detected, and whose concentrations were highest, were the three herbicides atrazine, metolachlor, and simazine, and two herbicide metabolites (the atrazine metabolite deethylatrazine, and the metolachlor metabolite metolachlor ESA). Most of these compounds, or their parent compounds, are used on corn or other row crops. Median total pesticide and metabolite concentration for each network ranged from less than 0.02 µg/L for the New York City reservoirs network to more than 2 µg/L for the western New York reservoir network; the median for