On May 18, 1980, Mt. St. Helens erupted, coating the stream substrates across eastern Washington and Northern Idaho with two or more inches of ash, and creating catastrophic drift of the benthos. One year later, a macroinvertebrate survey was conducted along a reach of Idaho’s upper Palouse River.  Its purpose was to investigate the restoration and re-colonization of benthic habitats as evidenced by the specificity of species-habitat associations.  To maximize n and improve the ability to distinguish habitat affinities, a scaled-down, 1/4 square-foot Hess sampler was used to collect a large number of non-composited samples (48 each from riffles, runs, and pools).  The majority of the commonly collected taxa showed clear macro-habitat affinities:  for example the free-swimming Baetis tricaudatus was restricted to riffles; however another free swimming baetid, Centroptilum sp. avoided competition by keeping strictly to the runs and pools.  One of the Eukiefferiella species was only found on riffles, contrary to the run/pool life style of the other midges.  The community composition among the runs and pools was similar, while clear distinctions between the riffle and non-riffle habitats were found.  Microhabitat affinities were also found, the most notable being the strong association of Serratella teresa with the moss, Fontinalis.