The Sediment Quality Triad (SQT) approach to sediment quality evaluation was used to characterize and assess the extent of altered benthic invertebrate assemblages, sediment contamination and toxicity in Lakes Sammamish, Washington, and Union near Seattle, Washington. These lakes lie along an urban and industrial development gradient with Lake Union being the most impacted, followed by Lakes Washington and Sammamish. Synoptic sediment samples from 58 stations were collected in 1999-2001, analyzed for chemical contaminants, used to conduct mortality tests on Chironomus tentans and Hyalella azteca, growth tests on C. tentans, and evaluated for benthic community composition. All data types (bioassay, sediment chemistry, and benthos) were analyzed separately, and then related to each other to identify contaminants potentially responsible for biological effects. All lines of evidence indicated that Lake Union was the most altered, followed by Lake Washington, and Lake Sammamish.