In 1988 an increase in goldfish (Carassius auratus) abundance was observed in the upper Mississippi River (UMR). From 1976 through 1992, at least 11 sites were sampled annually between river mile (RM)-301 and RM-575. From 1976 to 1987 only nine goldfish were collected in 211 hours of electrofishing, while from 1988 to 1992, 283 goldfish were collected in 66 hours of sampling effort. In the peak year, 1989, 108 goldfish were collected, while by 1992 only five were recorded. The change in goldfish abundance was most evident in navigation Pool 19 and in upper Pool 20, immediately downstream of Lock and Dam 19. Goldfish were also collected from four tributaries of Pool 19, during 1989. Goldfish had not been collected from these streams prior to 1988. Low flow in 1988 and 1989 coupled with elevated water temperatures in 1988 resulted in conditions conducive to rapid growth and reproduction of goldfish. Aquatic macrophytes in Pool 19 provided additional favorable habitat. Little information is available documenting the direct effects of goldfish on native fishes, but goldfish hybridize with the commercially valuable common carp (Cyprinus carpio). An increase in abundance of the hybrids followed the initial proliferation of goldfish. Although the overall effect of goldfish on the UMR fisheries is unknown, this episodic event may reflect changes in other biota during drought. © 1996, Copyright Taylor & Francis Group, LLC.