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Wildlife Service (1987a). The term 'post-larval fishes', as used here, refers only to YOY of large-size species such as Colorado squawfish, and in addition, includes juveniles and adults of small-size species such as fathead minnows, mosquitofish, etc. Correlations were performed on annual peak flow (mean flow of the highest day) versus annual mean number of larvae per sample, and annual peak flow versus annual mean number of post- larval fish per 100 m2 seined. Data for species that mature within the first year of life were first log-transformed because trends indicated that the increase in number of some species was more exponential than linear. We expect that the degree of increase from one year to the next in rapidly maturing species would be related to the number of adults that survived from the previous year. For late-maturing species, year-to-year variation in adult numbers is probably not great, and exponential-like increases in young were not noted. For these species, catch rates were first transformed to geometric means to improve normality of the data,(see McAda and Kaeding 1989). The reaches were analyzed separately because each had a different flow regime. Our results indicate a relationship between abundance of larval and post-larval fishes and peak flow exists for cer- tain species but not for others and the strength of these relationships varies among reaches. Larvae. Those native species that showed a consistent response to high flows in the three reaches were bluehead sucker and speckled dace; the introduced species were fathead minnow, sand shiner and red shiner (Table 2). Catch rates of larvae of the two native species increased with in- creased peak flow while those of the three introduced minnows decreased. Abundance of Colorado squawfish larvae increased with increased peak flow 16