The downstream effects of channelization and agricultural drainage development were evaluated in southwestern Minnesota by comparing benthic invertebrate populations in streams heavily modified by channelization and agricultural drainage development in upstream areas with those not so modified. Physicochemical characteristics, as well as invertebrate populations, were observed in relatively undisturbed downstream reaches. Turbidity, total alkalinity, and timing of discharge were similar in all streams. Species compositions of benthic invertebrates were similar in all streams, and there were no significant differences in total, seasonal, or monthly levels of standing stock in either numbers or biomass between modified and unmodified streams. Invertebrate drift, both insects and total invertebrates, was similar in all streams. Some differences in individual taxa were observed, but these were related to localized differences between streams, rather than to drainage development. Specific differences included higher numbers in drift of the snail Physa gyrina and the amphipod Hyalella azteca in one modified stream, apparently the result of more suitable upstream habitat in drainage ditches. It was concluded that, in these agricultural areas, the impact of upstream drainage development on benthic invertebrates in natural downstream reaches was negligible.