An Impact Source Determination method, used to identify point and nonpoint sources of impacts to stream water quality on the basis of benthic macroinvertebrates, was examined for concordance with impairment sources inferred from chemical and physical site characteristics, watershed characteristics, and biomonitoring results collected from 26 sites in the Hudson River Basin during 1993–94. Most classifications agreed with the resulting interpretations; site locations on Canonical Correspondence Analysis triplots corresponded with interpretation of environmental gradients as (1) overall pollution including organic enrichment and contaminants from point and nonpoint sources, (2) nonpoint nutrients from both agricultural and urban sources, and (3) sediment and suspended organic carbon from agricultural runoff. High-level taxonomic resolution was important in identifying the environmental gradients, and may be necessary for impairment source identification.