Near-shore variation in number and weight of riffle insects was shown to be affected by changes in depth (15, 30 and 45 cm) and current velocity, interacting with date and station of sampling. This differential littoral distribution of riffle insects resulted in variation of the littoral community structure. In the non-fluctuating system, community diversity and diversity per individual decreased with increasing depths to 45 cm and current velocity to 1.1m/sec. Insects tested in the laboratory demonstrated variability in temperature-exposure tolerances. The case-bearing caddisfly, Dicosmoecus sp., was generally more tolerant than the stonefly, Pteronarcys californica, at most temperature regimes. (Modified author abstract)