Late instarBrachvcentrus americanuslarvae were collected just prior to and during normally high spring runoff; adults were collected immediately following runoff; and early instar larvae appeared during the late summer low flow period of September and October.Brachvcentrus occidentalisadults were collected prior to normal spring runoff and early instar were first collected following runoff during moderate flows of July and August. Both strategies helped these species avoid stresses of high water velocities and sediment scouring often associated with spring runoff. During the study period, yearly high stream flows and maximum sediment movement occurred during summer flushing releases from Electric Lake, rather than the normal spring runoff period. Increased stream discharges with associated sediment movement that occurred when early instarBrachvcentruslarvae were present, appear to have had noticeable negative affects. Whatever the cause, following these occurrences, either species having early instar larvae present during the occurrence, showed noticeable reductions in numbers of larvae. Inorganic suspended sediments associated with these flows could have interfered with feeding, scoured larvae off substrates, hindered respiration, triggered a drift behavior or possibly a combination of these and other factors. Whatever the cause,B. occidentalisnumbers were depressed and the distribution of numbers over the various larval body lengths was disrupted following flushes of 1975, 1979 and 1982.Brachvcentrus americanuslarvae did not show the same negative responses following these occurrences.