A standardized stream monitoring program conducted on the Altamaha River, Georgia, from 1988 to 1992 was successful in detecting substantial changes in sport fish populations. Flathead catfish (Pylodictus olivaris) electrofishing catch rates generally increased from 1988 to 1992 reaching a peak CPUE of 90 fish per hour in 1990. CPUE of flathead catfish was significantly different (P < 0.05) between years and sites. Percent composition of flathead catfish in ictalurid samples doubled over the 5-year study period. A concurrent decrease in native bullhead populations was observed in annual creel and electrofishing surveys. Redbreast sunfish catch rates precipitously declined in both electrofishing samples and creel surveys taken from 1988 to 1992. Differences in mean CPUE of redbreast sunfish were significant (P < 0.05). Annual monitoring results suggest that the invasion and subsequent rapid expansion of flathead catfish in the Altamaha River has affected native sport fish populations.